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The physiological impact of soccer on elite female playersand the effects of active recovery training
Örebro Studies in Sport Sciences 8
Helena Andersson
The physiological impact of soccer on elite female playersand the effects of active recovery training
© Helena Andersson, 2010
Title: The physiological impact of soccer on elite female playersand the effects of active recovery training.
Publisher: Örebro University 2010www.publications.oru.se
Editor: Heinz [email protected]
Printer: intellecta infolog, Kållered 05/2010
issn 1654-7535 isbn 978-91-7668-735-2
ABSTRACT
Female soccer is becoming more popular and professional in the world. There are, however, limited
scientific data available on how elite female players respond to physical stress during soccer games.
An effective recovery strategy following a game is important, because there are few recovery days
between the games in international tournaments. The present thesis, which was designed to mirror a
competitive situation, aimed to investigate changes in several physiological systems occurring in
female elite players in response to two soccer games. It also aimed to investigate the effects of active
recovery training on the recovery of several physiological systems. METHODS: Two elite female
soccer teams played two 90-min games separated by 72 h active or passive recovery. The active
recovery training (cycling at 60% HRpeak, resistance training at <50% 1RM) lasted one hour and
was performed 22 and 46 h after the first game. Countermovement jump (CMJ), 20-m sprint time
and isokinetic knee strength were measured before, immediately, 5, 21, 45, 51, and 69 h after the first
game, and immediately after the second game. The physical stress markers (CK, urea), oxidative stress
markers (e.g., GSSG, lipid peroxidation), endogenous (e.g., UA, thiols) and dietary antioxidants (e.g.,
tocopherols, carotenoids) and a large battery of cytokines (e.g., IL-6, TNF-) were analysed in blood.
RESULTS: No significant differences were observed in the performance parameters, oxidative stress
and antioxidant levels or inflammatory response between the active and passive recovery groups.
Sprint and isokinetic knee strength were reduced by the same extent after both games. CMJ decreased
after the first game and remained reduced throughout the study period. Blood physical stress markers,
GSSG and endogenous antioxidants increased with similar amplitude after both games together with
unchanged lipid peroxidation. The dietary antioxidants showed either a rapid and persistent change
(e.g., tocopherols) or a delayed rise (carotenoids) after the first game. A transient increase occurred in
several pro- (e.g., IL-12, TNF-α, MCP-1), anti-inflammatory (e.g., IL-4, IL-10, INF-α) and mixed (IL-
6) cytokines after the first game. Fewer cytokines increased in response to the second game.
CONCLUSION: Two repeated elite female soccer games separated by 72 h induced similar acute
changes in several physiological parameters. After the first game, differences in the recovery pattern of
the neuromuscular parameters occurred. In particular, the slow recovery of CMJ indicates that special
attention should be devoted to the training of explosive force. Furthermore, the recruitment of
antioxidants in response to the transient increase in GSSG resulted in the maintenance of the redox-
balance in female players. Similarly, a strong and balanced pro- and anti-inflammatory cytokine
response occurred after one single female soccer game. The consequences of the dampened cytokine
response during repeated soccer games are, however, unknown. In general, the majority of the
parameters had recovered prior to the second game and the physiological alterations induced by the
first game did not affect the performance of players in the second game. Finally, active recovery
training conducted after a soccer game does not accelerate the recovery time for neuromuscular,
oxidative stress, antioxidant and inflammatory responses in elite female players.
KEY WORDS: Football, Training, Recovery, Intermittent exercise
Helena Andersson, School of Health and Medical Sciences,
Örebro University, SE-70182, Örebro, Sweden. e-mail: [email protected]
ABSTRACT
Female soccer is becoming more popular and professional in the world. There are, however, limited
scientific data available on how elite female players respond to physical stress during soccer games.
An effective recovery strategy following a game is important, because there are few recovery days
between the games in international tournaments. The present thesis, which was designed to mirror a
competitive situation, aimed to investigate changes in several physiological systems occurring in
female elite players in response to two soccer games. It also aimed to investigate the effects of active
recovery training on the recovery of several physiological systems. METHODS: Two elite female
soccer teams played two 90-min games separated by 72 h active or passive recovery. The active
recovery training (cycling at 60% HRpeak, resistance training at <50% 1RM) lasted one hour and
was performed 22 and 46 h after the first game. Countermovement jump (CMJ), 20-m sprint time
and isokinetic knee strength were measured before, immediately, 5, 21, 45, 51, and 69 h after the first
game, and immediately after the second game. The physical stress markers (CK, urea), oxidative stress
markers (e.g., GSSG, lipid peroxidation), endogenous (e.g., UA, thiols) and dietary antioxidants (e.g.,
tocopherols, carotenoids) and a large battery of cytokines (e.g., IL-6, TNF-) were analysed in blood.
RESULTS: No significant differences were observed in the performance parameters, oxidative stress
and antioxidant levels or inflammatory response between the active and passive recovery groups.
Sprint and isokinetic knee strength were reduced by the same extent after both games. CMJ decreased
after the first game and remained reduced throughout the study period. Blood physical stress markers,
GSSG and endogenous antioxidants increased with similar amplitude after both games together with
unchanged lipid peroxidation. The dietary antioxidants showed either a rapid and persistent change
(e.g., tocopherols) or a delayed rise (carotenoids) after the first game. A transient increase occurred in
several pro- (e.g., IL-12, TNF-α, MCP-1), anti-inflammatory (e.g., IL-4, IL-10, INF-α) and mixed (IL-
6) cytokines after the first game. Fewer cytokines increased in response to the second game.
CONCLUSION: Two repeated elite female soccer games separated by 72 h induced similar acute
changes in several physiological parameters. After the first game, differences in the recovery pattern of
the neuromuscular parameters occurred. In particular, the slow recovery of CMJ indicates that special
attention should be devoted to the training of explosive force. Furthermore, the recruitment of
antioxidants in response to the transient increase in GSSG resulted in the maintenance of the redox-
balance in female players. Similarly, a strong and balanced pro- and anti-inflammatory cytokine
response occurred after one single female soccer game. The consequences of the dampened cytokine
response during repeated soccer games are, however, unknown. In general, the majority of the
parameters had recovered prior to the second game and the physiological alterations induced by the
first game did not affect the performance of players in the second game. Finally, active recovery
training conducted after a soccer game does not accelerate the recovery time for neuromuscular,
oxidative stress, antioxidant and inflammatory responses in elite female players.
KEY WORDS: Football, Training, Recovery, Intermittent exercise
Helena Andersson, School of Health and Medical Sciences,
Örebro University, SE-70182, Örebro, Sweden. e-mail: [email protected]
LIST OF PUBLICATIONS
I Andersson H, Raastad T, Nilsson J, Paulsen G, Garthe I, Kadi F (2008). Neuromuscular fatigue and recovery in elite female soccer: Effects of active recovery. Med Sci Sports Exerc 40 (2), 372–380.
II Andersson H, Karlsen A, Blomhoff R, Raastad T, Kadi F (2009). Plasma
antioxidant responses and oxidative stress following a soccer game in elite female players. Scand J Med Sci Sports 23. E-publication ahead of print version.
III Andersson H, Bøhn S-K, Paulsen G, Raastad T, Blomhoff R, Kadi F (2009).
Differences in the inflammatory plasma cytokine response following two elite female soccer games separated by a 72-h recovery. Scand J Med Sci Sports 17. E-publication ahead of print version.
IV Andersson H, Karlsen A, Blomhoff R, Raastad T, Kadi F. Active recovery
training does not affect the antioxidant response to soccer games in elite female players. Accepted for publication in Br J Nutr. May 19, 2010.
LIST OF PUBLICATIONS
I Andersson H, Raastad T, Nilsson J, Paulsen G, Garthe I, Kadi F (2008). Neuromuscular fatigue and recovery in elite female soccer: Effects of active recovery. Med Sci Sports Exerc 40 (2), 372–380.
II Andersson H, Karlsen A, Blomhoff R, Raastad T, Kadi F (2009). Plasma
antioxidant responses and oxidative stress following a soccer game in elite female players. Scand J Med Sci Sports 23. E-publication ahead of print version.
III Andersson H, Bøhn S-K, Paulsen G, Raastad T, Blomhoff R, Kadi F (2009).
Differences in the inflammatory plasma cytokine response following two elite female soccer games separated by a 72-h recovery. Scand J Med Sci Sports 17. E-publication ahead of print version.
IV Andersson H, Karlsen A, Blomhoff R, Raastad T, Kadi F. Active recovery
training does not affect the antioxidant response to soccer games in elite female players. Accepted for publication in Br J Nutr. May 19, 2010.
LIST OF ABBREVIATION
AA Ascorbic Acid ANOVA The Analysis of Variance CHO Carbohydrate CK Creatine Kinase CMJ Countermovement jump CV Coefficient of variance d-ROMs The Diacrons Reactive Oxygen Metabolites EDTA Ethylenediaminetetraacetic acid ELISA Enzyme-linked immunosorbent assay FIFA Fédération Internationale de Football Association
FRAP Ferric Reducing/Antioxidant Power Assay GM-CSF Granolyte/Macrophage Colony-Stimulating Factor GSH Reduced glutathione GSSG Oxidised glutathione HIR High Intensity Running HPCL High Performance Liquid Chromatography HR Heart Rate IL Interleukin IL-1 RA IL-1 Receptor Antagonist INF Interferon IP ImmunoProtein MCP-1 Monocyte Chemoattractant Protein-1 MDA Malondialdehyde MIG The Monokine induced by Interferon-Gamma MIP Macrophage Inflammatory Protein NIST 970 SRM
National Institute of Standards and Technology, Standardized Reference Material nr 970
RANTES Regulated upon Activation Normal T-cell Expressed and Secreted RNS Reactive Nitrogen Species ROS Reactive Oxygen Species TBARS Thioburbiuric acid-reactive substances TGSH Total Glutathione TNF Tumor Necrosis Factor UA Uric Acid UEFA Union of European Football Associations
2
•
VO max Maximal oxygen uptake
LIST OF ABBREVIATION
AA Ascorbic Acid ANOVA The Analysis of Variance CHO Carbohydrate CK Creatine Kinase CMJ Countermovement jump CV Coefficient of variance d-ROMs The Diacrons Reactive Oxygen Metabolites EDTA Ethylenediaminetetraacetic acid ELISA Enzyme-linked immunosorbent assay FIFA Fédération Internationale de Football Association
FRAP Ferric Reducing/Antioxidant Power Assay GM-CSF Granolyte/Macrophage Colony-Stimulating Factor GSH Reduced glutathione GSSG Oxidised glutathione HIR High Intensity Running HPCL High Performance Liquid Chromatography HR Heart Rate IL Interleukin IL-1 RA IL-1 Receptor Antagonist INF Interferon IP ImmunoProtein MCP-1 Monocyte Chemoattractant Protein-1 MDA Malondialdehyde MIG The Monokine induced by Interferon-Gamma MIP Macrophage Inflammatory Protein NIST 970 SRM
National Institute of Standards and Technology, Standardized Reference Material nr 970
RANTES Regulated upon Activation Normal T-cell Expressed and Secreted RNS Reactive Nitrogen Species ROS Reactive Oxygen Species TBARS Thioburbiuric acid-reactive substances TGSH Total Glutathione TNF Tumor Necrosis Factor UA Uric Acid UEFA Union of European Football Associations
2
•
VO max Maximal oxygen uptake
TABLE OF CONTENT
1 INTRODUCTION ..................................................................................11
1.1 BACKGROUND: FEMALE SOCCER ..............................................11
1.2 PHYSIOLOGICAL ASPECTS OF FEMALE SOCCER .....................12
1.2.1 Characteristics of female soccer players ............................................12
1.2.2 Workload during games ....................................................................12
1.2.3 The effects of a soccer game on performance and ............................ 13 neuromuscular fatigue markers
1.2.4 The effects of a soccer game on blood markers ................................14 of physical stress
1.3 EXERCISE, OXIDATIVE STRESS AND ANTIOXIDANTS ...........14
1.3.1 Oxidative stress .................................................................................14
1.3.2 Antioxidant compounds .................................................................... 15
1.3.3 The effects of a soccer game on oxidative stress .............................. 16 and antioxidant compounds
1.4 THE INFLAMMATORY RESPONSE TO EXERCISE .....................17
1.4.1 Cytokines and chemokines ................................................................17
1.4.2 The effects of a soccer game on the infl ammatory cell response .......18
1.5 ACTIVE RECOVERY STRATEGIES IN SOCCER ..........................19
2 AIMS OF THE THESIS .........................................................................21
3 METHODS & MATERIALS ...................................................................23
3.1 SUBJECTS ........................................................................................23
3.2 STUDY DESIGN ...............................................................................23
3.3 ACTIVE RECOVERY TRAINING ..................................................24
3.4 DIET ................................................................................................. 25
3.5 EVALUATION OF WORKLOAD DURING THE GAMES ..............26
3.6 BLOOD SAMPLING ........................................................................27
3.7 NEUROMUSCULAR FATIGUE AND BLOOD ..............................27 MARKERS OF PHYSICAL STRESS
3.7.1 Sprint, CMJ and isokinetic strength tests ..........................................27
3.7.2 Perceived muscle soreness ..................................................................28
3.7.3 Blood markers of physical stress; CK, urea, .....................................29 uric acid and glucose
Innehåll Helena Andersson.indd 9 2010-05-19 13.05
11
1 INTRODUCTION
1.1 BACKGROUND: FEMALE SOCCER
In the early eighteenth century, female soccer games were played as an annual ritual
between married and single women in Scotland (Williamson 1991). Female soccer
became increasingly popular during World War I when games were organised by
factory workers in England to raise money for charity (Williamson 1991). In 1920,
for example, a game was played with a crowd of 53,000 people in the stands
(Newsham 1997). In 1921, however, the English Football Association first decided
that permission was necessary for clubs to organise female soccer games and later
forbade females from playing soccer stating that it was “quite unsuitable for females
and should not be encouraged” (Williamson 1991). The ban on female soccer was
not lifted until 1971.
Today, female soccer is one of the fastest growing sports and has 26 million
participants around the world (FIFA 2007). For example, Germany has over one
million registered female soccer players (Deutscher Fussball-Bund 2009), while both
Sweden and Denmark have approximately 60,000 registered players (Dansk
Boldspil-Union 2009; Svenska Fotbollförbundet 2008). In 2006, 448 female
international games were played in 134 countries (FIFA 2007). Moreover, several
countries have leagues with full-time professional players. For national teams, the
FIFA Women’s World Cup, the Olympic Games and the UEFA Women’s
Championship are the most prestigious tournaments. At the club level, in addition to
the domestic national leagues, the most prestigious competition is the UEFA
Women’s Champions League.
During international female soccer tournaments, such as the FIFA Women’s
World Cup and Olympic games, only two days of recovery are allowed between
games compared to four to five days of recovery in male soccer tournaments. There
are no reports, as far as we know, investigating whether two days of recovery after a
game is sufficient recovery time for female players. Due to the short period of time
separating two soccer games, it is important to optimise the recovery of players. It is
therefore important to study the impact of a soccer game on several physiological
systems in order to design effective recovery strategies. Such information about elite
female soccer players is scarce, however.
3.8 OXIDATIVE STRESS MARKERS AND .........................................29 ANTIOXIDANT COMPOUNDS
3.8.1 Oxidative stress markers ...................................................................29
3.8.2 Antioxidant compounds ....................................................................30
3.9 INFLAMMATORY CELLS AND CYTOKINE RESPONSE............ 31
3.9.1 Leukocyte cell count ......................................................................... 31
3.9.2 Cytokine analysis .............................................................................. 31
3.10 STATISTICAL ANALYSES...............................................................32
3.11 ETHICAL APPROVAL ..................................................................... 33
4 RESULTS AND DISCUSSION .................................................................. 35
4.1 WORKLOAD DURING THE GAMES ............................................ 35
4.1.1 Main fi ndings .................................................................................... 35
4.1.2 Discussion. ........................................................................................36
4.2 NEUROMUSCULAR FATIGUE AND BLOOD MARKERS OF .....37 PHYSICAL STRESS AFTER ELITE FEMALE SOCCER GAMES (PAPER I)
4.2.1 Main fi ndings ....................................................................................37
4.2.3 Discussion ......................................................................................... 39
4.3 OXIDATIVE STRESS MARKERS AND ANTIOXIDANT .............40 COMPOUNDS AFTER ELITE FEMALE SOCCER GAMES (PAPER II AND IV).
4.3.1 Main fi ndings ....................................................................................40
4.3.2 Discussion .........................................................................................42
4.4 INFLAMMATORY RESPONSE AFTER ELITE .............................46 FEMALE SOCCER GAMES (PAPER III)
4.4.1 Main fi ndings ....................................................................................46
4.4.2 Discussion .........................................................................................47
5 CONCLUSIONS ...................................................................................51
5.1 MAIN FINDINGS OF THE THESIS ...............................................51
5.2 IMPLICATIONS ...............................................................................52
5.3 STUDY STRENGTHS AND LIMITATIONS ...................................53
5.4 FUTURE DIRECTIONS ................................................................... 55
6 ACKNOWLEDGEMENTS .......................................................................57
SVENSK SAMMANFATTNING ................................................................59
REFERENCES.............................................................................................61
Innehåll Helena Andersson.indd 10 2010-05-19 13.05
The physiological impact of soccer on elite... ✍ helena andersson I 11
11
1 INTRODUCTION
1.1 BACKGROUND: FEMALE SOCCER
In the early eighteenth century, female soccer games were played as an annual ritual
between married and single women in Scotland (Williamson 1991). Female soccer
became increasingly popular during World War I when games were organised by
factory workers in England to raise money for charity (Williamson 1991). In 1920,
for example, a game was played with a crowd of 53,000 people in the stands
(Newsham 1997). In 1921, however, the English Football Association first decided
that permission was necessary for clubs to organise female soccer games and later
forbade females from playing soccer stating that it was “quite unsuitable for females
and should not be encouraged” (Williamson 1991). The ban on female soccer was
not lifted until 1971.
Today, female soccer is one of the fastest growing sports and has 26 million
participants around the world (FIFA 2007). For example, Germany has over one
million registered female soccer players (Deutscher Fussball-Bund 2009), while both
Sweden and Denmark have approximately 60,000 registered players (Dansk
Boldspil-Union 2009; Svenska Fotbollförbundet 2008). In 2006, 448 female
international games were played in 134 countries (FIFA 2007). Moreover, several
countries have leagues with full-time professional players. For national teams, the
FIFA Women’s World Cup, the Olympic Games and the UEFA Women’s
Championship are the most prestigious tournaments. At the club level, in addition to
the domestic national leagues, the most prestigious competition is the UEFA
Women’s Champions League.
During international female soccer tournaments, such as the FIFA Women’s
World Cup and Olympic games, only two days of recovery are allowed between
games compared to four to five days of recovery in male soccer tournaments. There
are no reports, as far as we know, investigating whether two days of recovery after a
game is sufficient recovery time for female players. Due to the short period of time
separating two soccer games, it is important to optimise the recovery of players. It is
therefore important to study the impact of a soccer game on several physiological
systems in order to design effective recovery strategies. Such information about elite
female soccer players is scarce, however.
3.8 OXIDATIVE STRESS MARKERS AND .........................................29 ANTIOXIDANT COMPOUNDS
3.8.1 Oxidative stress markers ...................................................................29
3.8.2 Antioxidant compounds ....................................................................30
3.9 INFLAMMATORY CELLS AND CYTOKINE RESPONSE............ 31
3.9.1 Leukocyte cell count ......................................................................... 31
3.9.2 Cytokine analysis .............................................................................. 31
3.10 STATISTICAL ANALYSES...............................................................32
3.11 ETHICAL APPROVAL ..................................................................... 33
4 RESULTS AND DISCUSSION .................................................................. 35
4.1 WORKLOAD DURING THE GAMES ............................................ 35
4.1.1 Main fi ndings .................................................................................... 35
4.1.2 Discussion. ........................................................................................36
4.2 NEUROMUSCULAR FATIGUE AND BLOOD MARKERS OF .....37 PHYSICAL STRESS AFTER ELITE FEMALE SOCCER GAMES (PAPER I)
4.2.1 Main fi ndings ....................................................................................37
4.2.3 Discussion ......................................................................................... 39
4.3 OXIDATIVE STRESS MARKERS AND ANTIOXIDANT .............40 COMPOUNDS AFTER ELITE FEMALE SOCCER GAMES (PAPER II AND IV).
4.3.1 Main fi ndings ....................................................................................40
4.3.2 Discussion .........................................................................................42
4.4 INFLAMMATORY RESPONSE AFTER ELITE .............................46 FEMALE SOCCER GAMES (PAPER III)
4.4.1 Main fi ndings ....................................................................................46
4.4.2 Discussion .........................................................................................47
5 CONCLUSIONS ...................................................................................51
5.1 MAIN FINDINGS OF THE THESIS ...............................................51
5.2 IMPLICATIONS ...............................................................................52
5.3 STUDY STRENGTHS AND LIMITATIONS ...................................53
5.4 FUTURE DIRECTIONS ................................................................... 55
6 ACKNOWLEDGEMENTS .......................................................................57
SVENSK SAMMANFATTNING ................................................................59
REFERENCES.............................................................................................61
Innehåll Helena Andersson.indd 10 2010-05-19 13.05
12 I The physiological impact of soccer on elite... ✍ helena andersson
12
1.2 PHYSIOLOGICAL ASPECTS OF FEMALE SOCCER
1.2.1 1.2.1 1.2.1 1.2.1 CCCCharacharacharacharacteristicsteristicsteristicsteristics of female soccer players of female soccer players of female soccer players of female soccer players
The general characteristics of female soccer players have been extensively described
in the literature (Davis & Brewer 1993; Jensen & Larsson 1992; Rhodes & Mosher
1992; Stølen et al. 2005; Tamer et al. 1997; Todd et al. 2002; Tumilty & Darby
1992). These studies showed that average range in height (158-170 cm), weight (55-
65 kg), 2
•
VO max (47-58 mL.min-1.kg-1), vertical jump performance (31- 44 cm) and
20-m sprint time (3.00-3.31 s) vary among players in the various levels of
competition and the different positions of players in the field (Krustrup et al. 2005;
Mohr et al. 2008; Polman et al. 2004; Siegler et al. 2003; Stølen et al. 2005; Tumilty
& Darby 1992).
1.2.2 1.2.2 1.2.2 1.2.2 Workload during gamesWorkload during gamesWorkload during gamesWorkload during games
Heart rate and blood lactate levels. The workload during a female soccer game is
relatively high, but includes variations between players. The evaluation of heart rate
during games shows that the mean heart rate represents ~85% of HRpeak (average
range 161-177 bpm) and that the players may reach near maximum values (~97%
HRpeak; average range 171-205 bpm) several times during a game (Andersson et al.
2010; Davis & Brewer 1993; Krustrup et al. 2005). A blood lactate value of
approximately 5 mmol·L-1 is usually reported by the end of a game (Davis & Brewer
1993; Krustrup et al. 2010). However, somewhat higher lactate values can be found
after an intense work period during games (Krustrup et al. 2006). Both the mean
heart rate and blood lactate levels reported in female players are within the same
ranges of values reported in males (Bangsbo 1994).
Movement pattern analysis during games. The first reports on the movement pattern
during female soccer games showed that players covered an average distance of
8.5±2.2 km (Davis & Brewer 1993). More recent studies report total distances
around 10 km per game (Gabbett & Mulvey 2008; Hewitt et al. 2007; Krustrup et
al. 2005; Mohr et al. 2008) which is similar to data on male players (Krustrup et al.
2005; Mohr et al. 2008; Mohr et al. 2003b). The total distance includes a large
amount of walking and jogging (>50%). The distance covered in high intensity
13
running (HIR), which includes running speeds over 15 km/h and sprinting (>25
km/h), has therefore been suggested to be a better indicator of the physical stress
during a game. In a study by Mohr et al. (2008) it was shown that top international
female players covered an average of 1.7 km of HIR during a game. This differs from
elite male players who covered approximately 2-3 km in HIR during a game (Mohr
et al. 2003b). The amount of HIR performed by female soccer players is related to
the competition level and may range between 0.7-2.0 km during a game (Krustrup et
al. 2005; Mohr et al. 2008). It has also been reported that the same female player
covered a longer distance of HIR when playing an international game than when
playing a domestic league game (Andersson et al. 2010; Gabbett & Mulvey 2008).
Moreover, several studies show that the performance of players decreases towards
the end of a game (Gabbett & Mulvey 2008; Mohr et al. 2008; Mohr et al. 2003b).
For example, the distance in HIR during the second half is shorter compared to the
first half and this reduction in HIR occurs during the last 30 or 15 min of the game
(Andersson et al. 2010; Gabbett & Mulvey 2008; Mohr et al. 2003a; Mohr et al.
2008). Altogether, data on heart rate and movement pattern indicate the relatively
high workload of a female soccer game and the occurrence of fatigue by the end of
the games.
1.2.3 1.2.3 1.2.3 1.2.3 The effeThe effeThe effeThe effects of a soccer game on performance and neuromuscular fatigue cts of a soccer game on performance and neuromuscular fatigue cts of a soccer game on performance and neuromuscular fatigue cts of a soccer game on performance and neuromuscular fatigue
markersmarkersmarkersmarkers
Intensive game-activities affect the force-generating capacity of the neuromuscular
system. The evaluation of sprint capacity, jump ability and isokinetic knee strength
has been used to investigate neuromuscular fatigue (Raastad & Hallén 2000). There
is little information on neuromuscular fatigue and recovery following a soccer game,
especially in female soccer players. In males, it has been shown that sprint
performance, countermovement jump (CMJ), and isokinetic peak torque knee
extension and flexion are reduced after a single game and that these changes last up
to several days following a game (Ascensão et al. 2008; Fatouros et al. 2009;
Ispirlidis et al. 2008; Magalhães et al. 2010; Mohr et al. 2004; Raastad et al. 2002).
In female players, one report showed a decline in 30-m repeated sprint performance
but unchanged CMJ performance immediately after a single soccer game (Krustrup
et al. 2010). However, a second study on female players showed that CMJ
performance was reduced at 24 h but not immediately after a single soccer game
(Hoffman et al. 2003). Thus, few and inconsistent findings are available on changes
The physiological impact of soccer on elite... ✍ helena andersson I 13
12
1.2 PHYSIOLOGICAL ASPECTS OF FEMALE SOCCER
1.2.1 1.2.1 1.2.1 1.2.1 CCCCharacharacharacharacteristicsteristicsteristicsteristics of female soccer players of female soccer players of female soccer players of female soccer players
The general characteristics of female soccer players have been extensively described
in the literature (Davis & Brewer 1993; Jensen & Larsson 1992; Rhodes & Mosher
1992; Stølen et al. 2005; Tamer et al. 1997; Todd et al. 2002; Tumilty & Darby
1992). These studies showed that average range in height (158-170 cm), weight (55-
65 kg), 2
•
VO max (47-58 mL.min-1.kg-1), vertical jump performance (31- 44 cm) and
20-m sprint time (3.00-3.31 s) vary among players in the various levels of
competition and the different positions of players in the field (Krustrup et al. 2005;
Mohr et al. 2008; Polman et al. 2004; Siegler et al. 2003; Stølen et al. 2005; Tumilty
& Darby 1992).
1.2.2 1.2.2 1.2.2 1.2.2 Workload during gamesWorkload during gamesWorkload during gamesWorkload during games
Heart rate and blood lactate levels. The workload during a female soccer game is
relatively high, but includes variations between players. The evaluation of heart rate
during games shows that the mean heart rate represents ~85% of HRpeak (average
range 161-177 bpm) and that the players may reach near maximum values (~97%
HRpeak; average range 171-205 bpm) several times during a game (Andersson et al.
2010; Davis & Brewer 1993; Krustrup et al. 2005). A blood lactate value of
approximately 5 mmol·L-1 is usually reported by the end of a game (Davis & Brewer
1993; Krustrup et al. 2010). However, somewhat higher lactate values can be found
after an intense work period during games (Krustrup et al. 2006). Both the mean
heart rate and blood lactate levels reported in female players are within the same
ranges of values reported in males (Bangsbo 1994).
Movement pattern analysis during games. The first reports on the movement pattern
during female soccer games showed that players covered an average distance of
8.5±2.2 km (Davis & Brewer 1993). More recent studies report total distances
around 10 km per game (Gabbett & Mulvey 2008; Hewitt et al. 2007; Krustrup et
al. 2005; Mohr et al. 2008) which is similar to data on male players (Krustrup et al.
2005; Mohr et al. 2008; Mohr et al. 2003b). The total distance includes a large
amount of walking and jogging (>50%). The distance covered in high intensity
13
running (HIR), which includes running speeds over 15 km/h and sprinting (>25
km/h), has therefore been suggested to be a better indicator of the physical stress
during a game. In a study by Mohr et al. (2008) it was shown that top international
female players covered an average of 1.7 km of HIR during a game. This differs from
elite male players who covered approximately 2-3 km in HIR during a game (Mohr
et al. 2003b). The amount of HIR performed by female soccer players is related to
the competition level and may range between 0.7-2.0 km during a game (Krustrup et
al. 2005; Mohr et al. 2008). It has also been reported that the same female player
covered a longer distance of HIR when playing an international game than when
playing a domestic league game (Andersson et al. 2010; Gabbett & Mulvey 2008).
Moreover, several studies show that the performance of players decreases towards
the end of a game (Gabbett & Mulvey 2008; Mohr et al. 2008; Mohr et al. 2003b).
For example, the distance in HIR during the second half is shorter compared to the
first half and this reduction in HIR occurs during the last 30 or 15 min of the game
(Andersson et al. 2010; Gabbett & Mulvey 2008; Mohr et al. 2003a; Mohr et al.
2008). Altogether, data on heart rate and movement pattern indicate the relatively
high workload of a female soccer game and the occurrence of fatigue by the end of
the games.
1.2.3 1.2.3 1.2.3 1.2.3 The effeThe effeThe effeThe effects of a soccer game on performance and neuromuscular fatigue cts of a soccer game on performance and neuromuscular fatigue cts of a soccer game on performance and neuromuscular fatigue cts of a soccer game on performance and neuromuscular fatigue
markersmarkersmarkersmarkers
Intensive game-activities affect the force-generating capacity of the neuromuscular
system. The evaluation of sprint capacity, jump ability and isokinetic knee strength
has been used to investigate neuromuscular fatigue (Raastad & Hallén 2000). There
is little information on neuromuscular fatigue and recovery following a soccer game,
especially in female soccer players. In males, it has been shown that sprint
performance, countermovement jump (CMJ), and isokinetic peak torque knee
extension and flexion are reduced after a single game and that these changes last up
to several days following a game (Ascensão et al. 2008; Fatouros et al. 2009;
Ispirlidis et al. 2008; Magalhães et al. 2010; Mohr et al. 2004; Raastad et al. 2002).
In female players, one report showed a decline in 30-m repeated sprint performance
but unchanged CMJ performance immediately after a single soccer game (Krustrup
et al. 2010). However, a second study on female players showed that CMJ
performance was reduced at 24 h but not immediately after a single soccer game
(Hoffman et al. 2003). Thus, few and inconsistent findings are available on changes
14 I The physiological impact of soccer on elite... ✍ helena andersson
14
in neuromuscular parameters following a female soccer game. Additionally,
knowledge of the effects of repeated soccer games on neuromuscular parameters is
also limited.
1.2.41.2.41.2.41.2.4 The effects of a soccer game on blood markers of physical stress The effects of a soccer game on blood markers of physical stress The effects of a soccer game on blood markers of physical stress The effects of a soccer game on blood markers of physical stress
Creatine kinase (CK), urea and uric acid (UA) are biochemical makers used for the
evaluation of the physiological stress imposed by exercise. Increases in serum
creatine kinase levels in response to strenuous exercise may be a consequence of both
metabolic and mechanical stress (Brancaccio et al. 2007). Uric acid and urea are
markers of both enhanced nucleotide cycle turnover and the breakdown of amino
acids (Viru & Viru 2001). It has recently been shown that CK, urea and uric acid
increased and remained elevated several days after a single soccer game in male
players (Ascensão et al. 2008; Bangsbo 1994; Ispirlidis et al. 2008; Rowsell et al.
2009). Such information is not available for female players.
1.3 EXERCISE, OXIDATIVE STRESS AND ANTIOXIDANTS
1.3.11.3.11.3.11.3.1 Oxidative stress Oxidative stress Oxidative stress Oxidative stress
During high-intensity exercise the production of free radicals is enhanced (Davies et
al. 1982). Disturbances in the balance of free-radical production and antioxidant
defences in favour of free-radical production may lead to so called oxidative stress
(Nikolaidis et al. 2008). Under conditions of oxidative stress, free radicals may
damage various tissues including muscle cells (Davies et al. 1982). Free radicals do,
however, participate in many biological processes and their presence is essential for
normal cell function. For example, it has been shown that in unfatigued skeletal
muscle, free radicals have positive effects on the excitation-contraction coupling and
are essential for optimal contractile function (Reid 2001). Exercise-induced increases
in free radicals have also been suggested to act as signals to enhance the production
of enzymes relevant to cell defence and the adaptation to exercise (Gomez-Cabrera et
al. 2008b; Jackson 2008).
A free radical is a molecule or just a single atom with an unpaired electron which
makes it highly reactive. Any free radical involving oxygen can be referred to as
reactive oxygen species (ROS). Oxygen-centred free radicals contain two unpaired
15
electrons in their outer shell. As the free radicals in biological systems are derived
from or associated with the presence of molecular oxygen, free radicals in biological
systems are mostly ROS. Examples of ROS are the superoxide anion (O2-), the
peroxyl radical (ROO-) and the hydroxyl (- OH) (Asmus & Bonifacic 2000). The free
radicals may also derive from reactive nitrogen species (RNS) that includes nitric
oxide (NO-) and nitrogen dioxide (NO2-). ROS and RNS have a strong tendency to
extract electrons to reach a chemically more stable state and may cause damage to
cellular components (Ji 2000). The oxidative damage to cellular targets is
characterised by a progressive change or degradation of biomolecules as lipids,
proteins and DNA (Blomhoff 2005). Lipid peroxidation can thus be used as a
marker for the occurrence of oxidative stress.
1.3.2 1.3.2 1.3.2 1.3.2 Antioxidant compoundsAntioxidant compoundsAntioxidant compoundsAntioxidant compounds
In normal physiological conditions, the production of ROS and RNS is in a finely-
tuned equilibrium with the antioxidant system. This makes it possible for the body
to sustain a balanced redox status (Djordjevi 2004). The antioxidant system
includes enzymatic and non-enzymatic endogenous and dietary antioxidant
compounds. The enzymatic superoxide dismutase (SOD), catalase (CAT) and
glutathione peroxidase (GPx) are major parts of the endogenous antioxidant system
(Ji 2000). The non-enzymatic endogenous antioxidants such as uric acid and thiols
(including total glutathione, cysteine, homocysteine and cysteine-glycine) are
recognised as key physiological antioxidants that directly scavenge ROS and RNS
and also enhance the functional ability of other antioxidants (Hellsten et al. 1997;
Sen & Packer 2000). In addition, there are several potent antioxidants available in
the diet. Tocopherols (also known as vitamin E), for example, are efficient radical
scavengers that can convert superoxide, hydroxyl and lipid peroxyl radicals to less
reactive molecules (Powers et al. 2004). Ascorbic acid (AA) (also known as vitamin
C) is also an efficient antioxidant as it can directly scavenge ROS (Packer et al.
1979). Some carotenoid compounds are also effective dietary antioxidants. The
antioxidant function of a carontenoid is dependent on its structure and on the
specific chemical formation of the oxidizing species (Young & Lowe 2001). For
example, lycopene is one of the most potent antioxidants of the carotenoid family as
it can directly quench singlet oxygen (Di Mascio et al. 1989), while -carotene is
very reactive to peroxyl radicals (Burton & Ingold 1984) and zeaxanthin can limit
The physiological impact of soccer on elite... ✍ helena andersson I 15
14
in neuromuscular parameters following a female soccer game. Additionally,
knowledge of the effects of repeated soccer games on neuromuscular parameters is
also limited.
1.2.41.2.41.2.41.2.4 The effects of a soccer game on blood markers of physical stress The effects of a soccer game on blood markers of physical stress The effects of a soccer game on blood markers of physical stress The effects of a soccer game on blood markers of physical stress
Creatine kinase (CK), urea and uric acid (UA) are biochemical makers used for the
evaluation of the physiological stress imposed by exercise. Increases in serum
creatine kinase levels in response to strenuous exercise may be a consequence of both
metabolic and mechanical stress (Brancaccio et al. 2007). Uric acid and urea are
markers of both enhanced nucleotide cycle turnover and the breakdown of amino
acids (Viru & Viru 2001). It has recently been shown that CK, urea and uric acid
increased and remained elevated several days after a single soccer game in male
players (Ascensão et al. 2008; Bangsbo 1994; Ispirlidis et al. 2008; Rowsell et al.
2009). Such information is not available for female players.
1.3 EXERCISE, OXIDATIVE STRESS AND ANTIOXIDANTS
1.3.11.3.11.3.11.3.1 Oxidative stress Oxidative stress Oxidative stress Oxidative stress
During high-intensity exercise the production of free radicals is enhanced (Davies et
al. 1982). Disturbances in the balance of free-radical production and antioxidant
defences in favour of free-radical production may lead to so called oxidative stress
(Nikolaidis et al. 2008). Under conditions of oxidative stress, free radicals may
damage various tissues including muscle cells (Davies et al. 1982). Free radicals do,
however, participate in many biological processes and their presence is essential for
normal cell function. For example, it has been shown that in unfatigued skeletal
muscle, free radicals have positive effects on the excitation-contraction coupling and
are essential for optimal contractile function (Reid 2001). Exercise-induced increases
in free radicals have also been suggested to act as signals to enhance the production
of enzymes relevant to cell defence and the adaptation to exercise (Gomez-Cabrera et
al. 2008b; Jackson 2008).
A free radical is a molecule or just a single atom with an unpaired electron which
makes it highly reactive. Any free radical involving oxygen can be referred to as
reactive oxygen species (ROS). Oxygen-centred free radicals contain two unpaired
15
electrons in their outer shell. As the free radicals in biological systems are derived
from or associated with the presence of molecular oxygen, free radicals in biological
systems are mostly ROS. Examples of ROS are the superoxide anion (O2-), the
peroxyl radical (ROO-) and the hydroxyl (- OH) (Asmus & Bonifacic 2000). The free
radicals may also derive from reactive nitrogen species (RNS) that includes nitric
oxide (NO-) and nitrogen dioxide (NO2-). ROS and RNS have a strong tendency to
extract electrons to reach a chemically more stable state and may cause damage to
cellular components (Ji 2000). The oxidative damage to cellular targets is
characterised by a progressive change or degradation of biomolecules as lipids,
proteins and DNA (Blomhoff 2005). Lipid peroxidation can thus be used as a
marker for the occurrence of oxidative stress.
1.3.2 1.3.2 1.3.2 1.3.2 Antioxidant compoundsAntioxidant compoundsAntioxidant compoundsAntioxidant compounds
In normal physiological conditions, the production of ROS and RNS is in a finely-
tuned equilibrium with the antioxidant system. This makes it possible for the body
to sustain a balanced redox status (Djordjevi 2004). The antioxidant system
includes enzymatic and non-enzymatic endogenous and dietary antioxidant
compounds. The enzymatic superoxide dismutase (SOD), catalase (CAT) and
glutathione peroxidase (GPx) are major parts of the endogenous antioxidant system
(Ji 2000). The non-enzymatic endogenous antioxidants such as uric acid and thiols
(including total glutathione, cysteine, homocysteine and cysteine-glycine) are
recognised as key physiological antioxidants that directly scavenge ROS and RNS
and also enhance the functional ability of other antioxidants (Hellsten et al. 1997;
Sen & Packer 2000). In addition, there are several potent antioxidants available in
the diet. Tocopherols (also known as vitamin E), for example, are efficient radical
scavengers that can convert superoxide, hydroxyl and lipid peroxyl radicals to less
reactive molecules (Powers et al. 2004). Ascorbic acid (AA) (also known as vitamin
C) is also an efficient antioxidant as it can directly scavenge ROS (Packer et al.
1979). Some carotenoid compounds are also effective dietary antioxidants. The
antioxidant function of a carontenoid is dependent on its structure and on the
specific chemical formation of the oxidizing species (Young & Lowe 2001). For
example, lycopene is one of the most potent antioxidants of the carotenoid family as
it can directly quench singlet oxygen (Di Mascio et al. 1989), while -carotene is
very reactive to peroxyl radicals (Burton & Ingold 1984) and zeaxanthin can limit
16 I The physiological impact of soccer on elite... ✍ helena andersson
16
the diffusion of oxygen into membranes (Subczynski et al. 1991). Together, the
endogenous and dietary antioxidant compounds act in concert in the antioxidant
system against ROS and RNS (Powers & Sen 2000).
1.3.31.3.31.3.31.3.3 The effectThe effectThe effectThe effectssss of of of of a a a a soccer game on oxidative stress and antioxidant soccer game on oxidative stress and antioxidant soccer game on oxidative stress and antioxidant soccer game on oxidative stress and antioxidant
cocococommmmpounds pounds pounds pounds
During high intensity exercise, whole-body oxygen consumption may rise up to 20-
fold (Saltin & Åstrand 1967), while oxygen consumption in active muscles may
reach 100 times the resting level (Davies et al. 1982). About 95-98% of the total
oxygen consumption is used to produce ATP while 2-5% may undergo one electron
reduction with the production of ROS and RNS. It has been shown that exhaustive
exercise produces an excessive amount of ROS and RNS leading to oxidative stress
(Sastre et al. 1992). It is also suggested that in well-trained athletes only limited
oxidative stress occurs (Bloomer et al. 2006) which could be explained by a well-
adapted antioxidant defence system in trained athletes (Bloomer et al. 2006; Brites et
al. 1999; Cazzola et al. 2003).
Most studies on oxidative stress and antioxidant status following exercise have
used endurance exercise protocols (Aguiló et al. 2005; Cases et al. 2006; Tauler et al.
2005). Because the physiological load of intermittent exercise, such as soccer, differs
from continuous steady-state exercise, an extrapolation of data from continuous
steady-state exercise to intermittent exercise should be made with caution (Nieman
& Bishop 2006). Information on oxidative stress and antioxidants in soccer is,
however, limited. Recently, four reports showed the occurrence of increased
oxidative stress (increased lipid peroxidation) together with increased blood
antioxidant compounds following a single game in male players (Ascensão et al.
2008; Fatouros et al. 2009; Ispirlidis et al. 2008; Magalhães et al. 2010). These
studies indicate that elevations in antioxidant compounds following the games were
not able to quench an excessive increase in ROS production, thereby causing
oxidative stress. In these studies, however, only a limited number of antioxidant
compounds was analysed (uric acid and total antioxidant capacity). In two studies,
lipid peroxidation increased immediately after the game but a significant increase in
uric acid occurred only at 24 h after the game (Fatouros et al. 2009; Ispirlidis et al.
2008). In the third and forth study, total antioxidant capacity and uric acid increased
immediately after the game in parallel with increased lipid peroxidation (Ascensão et
al. 2008; Magalhães et al. 2010). The normalisation of total antioxidant capacity
17
occurred within 24 h, while uric acid remained elevated for more than 72 h
(Ascensão et al. 2008). It is suggested that one single soccer game is associated with
increases in the level of oxidative stress and deterioration of muscle performance
throughout a 72 h recovery period (Ascensão et al. 2008; Fatouros et al. 2009).
Knowledge on the impact of a soccer game on the antioxidant system, including
several members of the endogenous and dietary defence systems remains, however,
limited. Moreover, available data include measurements conducted in response to
one single soccer game. There is no data on the effects of repeated soccer games on
oxidative stress markers and antioxidant levels.
It is also important to note that studies on soccer-associated changes in oxidative
stress markers and antioxidant levels have been performed on male players
(Ascensão et al. 2008; Fatouros et al. 2009; Ispirlidis et al. 2008, Magalhães et al.
2010). As oestrogens may have a protective function against ROS during exercise in
untrained females (Akova et al. 2001), the existence of sex differences in the soccer-
associated oxidative stress and antioxidant responses cannot be excluded.
1.4 THE INFLAMMATORY RESPONSE TO EXERCISE
Exercise initiates an inflammatory response that is similar to that observed after
trauma or sepsis. This response includes both a systemic and a local immune
response (Pedersen 2000). The systemic response, also known as the acute phase
response, involves mobilisation of leukocytes, particularly neutrophil cells, into the
circulation (Malm et al. 2004; Ostrowski et al. 1999; Peake et al. 2005a). In
addition, lymphocytes (including natural killer cells) are also mobilised, and the
production of cytokines is increased after exercise (Cox et al. 2007; Peake et al.
2005a; Peake et al. 2005b).
1.4.11.4.11.4.11.4.1 Cytokines and chemokinesCytokines and chemokinesCytokines and chemokinesCytokines and chemokines
Cytokines are a group of proteins produced by immune and non-immune cells.
Many cytokines may be broadly classified as either pro-inflammatory (e.g.,
interleukin (IL)-12, INF- and TNF-α) or anti-inflammatory (e.g., INF-α, IL-10, IL-
4, IL-1), while some cytokines are suggested to have both pro-and anti-
inflammatory functions (e.g., IL-6) (Moldoveanu et al. 2001). The majority of
studies investigating the cytokine response during exercise have been conducted
The physiological impact of soccer on elite... ✍ helena andersson I 17
16
the diffusion of oxygen into membranes (Subczynski et al. 1991). Together, the
endogenous and dietary antioxidant compounds act in concert in the antioxidant
system against ROS and RNS (Powers & Sen 2000).
1.3.31.3.31.3.31.3.3 The effectThe effectThe effectThe effectssss of of of of a a a a soccer game on oxidative stress and antioxidant soccer game on oxidative stress and antioxidant soccer game on oxidative stress and antioxidant soccer game on oxidative stress and antioxidant
cocococommmmpounds pounds pounds pounds
During high intensity exercise, whole-body oxygen consumption may rise up to 20-
fold (Saltin & Åstrand 1967), while oxygen consumption in active muscles may
reach 100 times the resting level (Davies et al. 1982). About 95-98% of the total
oxygen consumption is used to produce ATP while 2-5% may undergo one electron
reduction with the production of ROS and RNS. It has been shown that exhaustive
exercise produces an excessive amount of ROS and RNS leading to oxidative stress
(Sastre et al. 1992). It is also suggested that in well-trained athletes only limited
oxidative stress occurs (Bloomer et al. 2006) which could be explained by a well-
adapted antioxidant defence system in trained athletes (Bloomer et al. 2006; Brites et
al. 1999; Cazzola et al. 2003).
Most studies on oxidative stress and antioxidant status following exercise have
used endurance exercise protocols (Aguiló et al. 2005; Cases et al. 2006; Tauler et al.
2005). Because the physiological load of intermittent exercise, such as soccer, differs
from continuous steady-state exercise, an extrapolation of data from continuous
steady-state exercise to intermittent exercise should be made with caution (Nieman
& Bishop 2006). Information on oxidative stress and antioxidants in soccer is,
however, limited. Recently, four reports showed the occurrence of increased
oxidative stress (increased lipid peroxidation) together with increased blood
antioxidant compounds following a single game in male players (Ascensão et al.
2008; Fatouros et al. 2009; Ispirlidis et al. 2008; Magalhães et al. 2010). These
studies indicate that elevations in antioxidant compounds following the games were
not able to quench an excessive increase in ROS production, thereby causing
oxidative stress. In these studies, however, only a limited number of antioxidant
compounds was analysed (uric acid and total antioxidant capacity). In two studies,
lipid peroxidation increased immediately after the game but a significant increase in
uric acid occurred only at 24 h after the game (Fatouros et al. 2009; Ispirlidis et al.
2008). In the third and forth study, total antioxidant capacity and uric acid increased
immediately after the game in parallel with increased lipid peroxidation (Ascensão et
al. 2008; Magalhães et al. 2010). The normalisation of total antioxidant capacity
17
occurred within 24 h, while uric acid remained elevated for more than 72 h
(Ascensão et al. 2008). It is suggested that one single soccer game is associated with
increases in the level of oxidative stress and deterioration of muscle performance
throughout a 72 h recovery period (Ascensão et al. 2008; Fatouros et al. 2009).
Knowledge on the impact of a soccer game on the antioxidant system, including
several members of the endogenous and dietary defence systems remains, however,
limited. Moreover, available data include measurements conducted in response to
one single soccer game. There is no data on the effects of repeated soccer games on
oxidative stress markers and antioxidant levels.
It is also important to note that studies on soccer-associated changes in oxidative
stress markers and antioxidant levels have been performed on male players
(Ascensão et al. 2008; Fatouros et al. 2009; Ispirlidis et al. 2008, Magalhães et al.
2010). As oestrogens may have a protective function against ROS during exercise in
untrained females (Akova et al. 2001), the existence of sex differences in the soccer-
associated oxidative stress and antioxidant responses cannot be excluded.
1.4 THE INFLAMMATORY RESPONSE TO EXERCISE
Exercise initiates an inflammatory response that is similar to that observed after
trauma or sepsis. This response includes both a systemic and a local immune
response (Pedersen 2000). The systemic response, also known as the acute phase
response, involves mobilisation of leukocytes, particularly neutrophil cells, into the
circulation (Malm et al. 2004; Ostrowski et al. 1999; Peake et al. 2005a). In
addition, lymphocytes (including natural killer cells) are also mobilised, and the
production of cytokines is increased after exercise (Cox et al. 2007; Peake et al.
2005a; Peake et al. 2005b).
1.4.11.4.11.4.11.4.1 Cytokines and chemokinesCytokines and chemokinesCytokines and chemokinesCytokines and chemokines
Cytokines are a group of proteins produced by immune and non-immune cells.
Many cytokines may be broadly classified as either pro-inflammatory (e.g.,
interleukin (IL)-12, INF- and TNF-α) or anti-inflammatory (e.g., INF-α, IL-10, IL-
4, IL-1), while some cytokines are suggested to have both pro-and anti-
inflammatory functions (e.g., IL-6) (Moldoveanu et al. 2001). The majority of
studies investigating the cytokine response during exercise have been conducted
18 I The physiological impact of soccer on elite... ✍ helena andersson
18
using continuous steady-state endurance exercise (Nieman et al. 2001; Ostrowski et
al. 1998b) or resistance exercise (Chan et al. 2003; Paulsen et al. 2005).
Chemokines (e.g., IL-8, MCP-1, GM-CSF, and MIG) have also been shown to be
up-regulated following endurance exercise (Åkerstrom et al. 2005; Ostrowski et al.
2001). Chemokines are chemotactic cytokines as they have the ability to induce
directed chemotaxis (Warren et al. 2004). The release of chemokines causes
leukocytes to adhere to vascular endothelium and subsequently to migrate into the
tissue spaces. Chemokines may also have broader functions including a role in
angiogenesis, collagen production and proliferation of hematopoietic precursor cells
(Kunkel 1999; Mantovani 1999). Some chemokines are considered pro-
inflammatory (e.g., IL-8) and induce the migration of leukocytes to an injured or
infected site (Laing & Secombes 2004).
1.4.1.4.1.4.1.4.2222 The effects of The effects of The effects of The effects of a soccer gamea soccer gamea soccer gamea soccer game on the inflammatory cell response on the inflammatory cell response on the inflammatory cell response on the inflammatory cell response
Few studies are available on the inflammatory cell response in soccer. Increases in
circulatory leukocyte cell count, mainly caused by increases in neutrophil cells, have
been reported in male players following soccer games (Ispirlidis et al. 2008; Malm et
al. 2004; Rowsell et al. 2009; Magalhães et al. 2010). There are currently three
studies available on the cytokine response in male players after soccer games. In one
study, IL-6 and IL-1b increased immediately after a single soccer game (Ispirlidis et
al. 2008). The authors did, however, report that IL-1b was below detection levels at
all other time points during the study period (Ispirlidis et al. 2008). A second study
reported increased levels of IL-6 and TNF- following a soccer specific intermittent
exercise protocol (Bishop et al. 2002). A third study revealed unchanged levels of IL-
6, IL-1b and IL-10 following four consecutive soccer games in youth players
(Rowsell et al. 2009). The cytokines in this study were measured more than 20 h
after the end of each game. Since alterations in cytokine levels can be brief and
rapidly normalised (Shephard 2002), the lack of soccer-associated changes in
cytokines in the study of Rowsell et al., (2009) can be due to the timing of blood
sample collection.
To our knowlegde there is no data on the response of a large number of
circulating pro-and anti-inflammatory cytokines following elite soccer, especially in
female players.
19
1.5 ACTIVE RECOVERY STRATEGIES IN SOCCER
The use of post-exercise recovery methods has gained more attention within sport
science research (Gill et al. 2006; King & Duffield 2009; Kinugasa & Kilding 2006;
Vaile et al. 2008a). Methods include contrast-water therapy (Cochrane 2004;
Kinugasa & Kilding 2006), active recovery training (Dawson et al. 2005; Gill et al.
2006) and cold-water immersion (Vaile et al. 2008b).
The scientific evidence supporting the effectiveness of such recovery strategies after
a soccer games is limited. In one study an active cool-down program performed
immediately after a single game had a positive effect on the recovery time for jump
and sprint performance as well as subjective muscle soreness (Reilly & Rigby 1999).
In male junior soccer players cold-water immersion performed immediately after
soccer games reduced the perception of general fatigue and leg soreness but had no
effect on a battery of physical performance tests, indices of muscle damage or
inflammatory markers (cytokines IL-1b, IL-6 and IL-10) (Rowsell et al. 2009).
Active recovery training performed one day after a soccer game is recommended in
order to achieve a faster return to a normal physical state (Barnett 2006; Reilly &
Ekblom 2005). To our knowledge, there are no studies evaluating the effectiveness of
active recovery training one day after a soccer game. The theoretical advantage of
active recovery training would be to accelerate the recovery time of neuromuscular
parameters and blood markers of physical stress and a quicker normalisation of the
redox status and immunological systems. It is hypothesized that this strategy is
necessary for optimal competitive performance and will help the players to cope with
high training and game loads (Barnett 2006; Reilly & Ekblom 2005). The
effectiveness of low-intensity training performed after a soccer game has not
previously been evaluated in elite players.
The physiological impact of soccer on elite... ✍ helena andersson I 19
18
using continuous steady-state endurance exercise (Nieman et al. 2001; Ostrowski et
al. 1998b) or resistance exercise (Chan et al. 2003; Paulsen et al. 2005).
Chemokines (e.g., IL-8, MCP-1, GM-CSF, and MIG) have also been shown to be
up-regulated following endurance exercise (Åkerstrom et al. 2005; Ostrowski et al.
2001). Chemokines are chemotactic cytokines as they have the ability to induce
directed chemotaxis (Warren et al. 2004). The release of chemokines causes
leukocytes to adhere to vascular endothelium and subsequently to migrate into the
tissue spaces. Chemokines may also have broader functions including a role in
angiogenesis, collagen production and proliferation of hematopoietic precursor cells
(Kunkel 1999; Mantovani 1999). Some chemokines are considered pro-
inflammatory (e.g., IL-8) and induce the migration of leukocytes to an injured or
infected site (Laing & Secombes 2004).
1.4.1.4.1.4.1.4.2222 The effects of The effects of The effects of The effects of a soccer gamea soccer gamea soccer gamea soccer game on the inflammatory cell response on the inflammatory cell response on the inflammatory cell response on the inflammatory cell response
Few studies are available on the inflammatory cell response in soccer. Increases in
circulatory leukocyte cell count, mainly caused by increases in neutrophil cells, have
been reported in male players following soccer games (Ispirlidis et al. 2008; Malm et
al. 2004; Rowsell et al. 2009; Magalhães et al. 2010). There are currently three
studies available on the cytokine response in male players after soccer games. In one
study, IL-6 and IL-1b increased immediately after a single soccer game (Ispirlidis et
al. 2008). The authors did, however, report that IL-1b was below detection levels at
all other time points during the study period (Ispirlidis et al. 2008). A second study
reported increased levels of IL-6 and TNF- following a soccer specific intermittent
exercise protocol (Bishop et al. 2002). A third study revealed unchanged levels of IL-
6, IL-1b and IL-10 following four consecutive soccer games in youth players
(Rowsell et al. 2009). The cytokines in this study were measured more than 20 h
after the end of each game. Since alterations in cytokine levels can be brief and
rapidly normalised (Shephard 2002), the lack of soccer-associated changes in
cytokines in the study of Rowsell et al., (2009) can be due to the timing of blood
sample collection.
To our knowlegde there is no data on the response of a large number of
circulating pro-and anti-inflammatory cytokines following elite soccer, especially in
female players.
19
1.5 ACTIVE RECOVERY STRATEGIES IN SOCCER
The use of post-exercise recovery methods has gained more attention within sport
science research (Gill et al. 2006; King & Duffield 2009; Kinugasa & Kilding 2006;
Vaile et al. 2008a). Methods include contrast-water therapy (Cochrane 2004;
Kinugasa & Kilding 2006), active recovery training (Dawson et al. 2005; Gill et al.
2006) and cold-water immersion (Vaile et al. 2008b).
The scientific evidence supporting the effectiveness of such recovery strategies after
a soccer games is limited. In one study an active cool-down program performed
immediately after a single game had a positive effect on the recovery time for jump
and sprint performance as well as subjective muscle soreness (Reilly & Rigby 1999).
In male junior soccer players cold-water immersion performed immediately after
soccer games reduced the perception of general fatigue and leg soreness but had no
effect on a battery of physical performance tests, indices of muscle damage or
inflammatory markers (cytokines IL-1b, IL-6 and IL-10) (Rowsell et al. 2009).
Active recovery training performed one day after a soccer game is recommended in
order to achieve a faster return to a normal physical state (Barnett 2006; Reilly &
Ekblom 2005). To our knowledge, there are no studies evaluating the effectiveness of
active recovery training one day after a soccer game. The theoretical advantage of
active recovery training would be to accelerate the recovery time of neuromuscular
parameters and blood markers of physical stress and a quicker normalisation of the
redox status and immunological systems. It is hypothesized that this strategy is
necessary for optimal competitive performance and will help the players to cope with
high training and game loads (Barnett 2006; Reilly & Ekblom 2005). The
effectiveness of low-intensity training performed after a soccer game has not
previously been evaluated in elite players.
20
21
2 AIMS OF THE THESIS
The overall aim of this thesis was to investigate physiological and biochemical
changes occurring in response to elite soccer games and to establish the time course
of recovery for the neuromuscular and immunological systems, and the redox status.
The physiological effects of active recovery training conducted during
the period separating two repeated soccer games were investigated in a
population of elite female players.
The specific aims were:
i.) to study the acute changes imposed by one soccer game on neuromuscular
fatigue parameters, blood markers of physical stress, the redox status and the
inflammatory response in elite female players (Study I, II and III)
ii.) to study the recovery pattern of neuromuscular fatigue parameters, blood
markers of physical stress, the redox status and the inflammatory response in
elite female players during a period of 72 h following the first soccer game
(study I, III, and IV)
iii.) to investigate the effects of low-intensity recovery training on the recovery
pattern of neuromuscular fatigue parameters, blood markers of physical stress,
the redox status and the inflammatory response in elite female players (study I,
III, and IV)
iv.) to compare the acute changes in neuromuscular fatigue parameters, blood
markers of physical stress, the redox status, and the inflammatory response
occurring after the first and second games (study I, III, IV).
The physiological impact of soccer on elite... ✍ helena andersson I 21
20
21
2 AIMS OF THE THESIS
The overall aim of this thesis was to investigate physiological and biochemical
changes occurring in response to elite soccer games and to establish the time course
of recovery for the neuromuscular and immunological systems, and the redox status.
The physiological effects of active recovery training conducted during
the period separating two repeated soccer games were investigated in a
population of elite female players.
The specific aims were:
i.) to study the acute changes imposed by one soccer game on neuromuscular
fatigue parameters, blood markers of physical stress, the redox status and the
inflammatory response in elite female players (Study I, II and III)
ii.) to study the recovery pattern of neuromuscular fatigue parameters, blood
markers of physical stress, the redox status and the inflammatory response in
elite female players during a period of 72 h following the first soccer game
(study I, III, and IV)
iii.) to investigate the effects of low-intensity recovery training on the recovery
pattern of neuromuscular fatigue parameters, blood markers of physical stress,
the redox status and the inflammatory response in elite female players (study I,
III, and IV)
iv.) to compare the acute changes in neuromuscular fatigue parameters, blood
markers of physical stress, the redox status, and the inflammatory response
occurring after the first and second games (study I, III, IV).
22 23
3 METHODS & MATERIALS
3.1 SUBJECTS
Twenty-two elite female soccer players (age 22±3 yrs; height 167±5 cm; weight 64±5
kg; VO2peak 55±3 ml.kg-1·min-1; HRpeak 198±6 beats·min-1) from two teams from
the highest divisions in Sweden and Norway played two international 90-min
friendly games separated by 72 h of active or passive recovery. Two defenders and
one midfielder were unable to take part in the testing sessions during the period
between the two games and were therefore not included in the data analyses. Because
the physical loading of goalkeepers differs from that of other players they were not
included in the analyses. Study I, on the neuromuscular fatigue and physical stress
changes associated with the soccer games included 17 players. Study II and IV, on
changes in oxidative stress markers and antioxidant levels included 16 players. Study
III, on inflammatory changes included 10 players due to financial restrictions.
3.2 STUDY DESIGN
The two games were played during a period of four days and were separated by two
days of either active or passive recovery. The same players in both teams participated
in both games and occupied the same field position. A randomised blocked design
was used to assign the players into an active recovery group (n=8) or a passive
recovery group (n=9). The players were matched for age, height, weight, maximal
oxygen consumption and field playing position. The active recovery training
consisted of a low-intensity training program (sub-maximal cycling at 60% of
HRpeak and low-intensity resistance training <50% 1 repetition max (RM))
performed at 22 h and 46 h after the first game. On game day, baseline values for
the performance parameters were obtained 3 h prior to the game. Subsequent
performance tests were carried out immediately, 5 h, 21 h, 27 h, 45 h, 51 h and 69 h
after the first game and immediately after the second game. Blood samples were
taken 3 h before, immediately after (within 15-20 min), 21 h, 45 h, 69 h after the
first game and immediately after the second game (Fig 1). Two days before the
commencement of the study, all subjects performed a maximal oxygen consumption
The physiological impact of soccer on elite... ✍ helena andersson I 23
22 23
3 METHODS & MATERIALS
3.1 SUBJECTS
Twenty-two elite female soccer players (age 22±3 yrs; height 167±5 cm; weight 64±5
kg; VO2peak 55±3 ml.kg-1·min-1; HRpeak 198±6 beats·min-1) from two teams from
the highest divisions in Sweden and Norway played two international 90-min
friendly games separated by 72 h of active or passive recovery. Two defenders and
one midfielder were unable to take part in the testing sessions during the period
between the two games and were therefore not included in the data analyses. Because
the physical loading of goalkeepers differs from that of other players they were not
included in the analyses. Study I, on the neuromuscular fatigue and physical stress
changes associated with the soccer games included 17 players. Study II and IV, on
changes in oxidative stress markers and antioxidant levels included 16 players. Study
III, on inflammatory changes included 10 players due to financial restrictions.
3.2 STUDY DESIGN
The two games were played during a period of four days and were separated by two
days of either active or passive recovery. The same players in both teams participated
in both games and occupied the same field position. A randomised blocked design
was used to assign the players into an active recovery group (n=8) or a passive
recovery group (n=9). The players were matched for age, height, weight, maximal
oxygen consumption and field playing position. The active recovery training
consisted of a low-intensity training program (sub-maximal cycling at 60% of
HRpeak and low-intensity resistance training <50% 1 repetition max (RM))
performed at 22 h and 46 h after the first game. On game day, baseline values for
the performance parameters were obtained 3 h prior to the game. Subsequent
performance tests were carried out immediately, 5 h, 21 h, 27 h, 45 h, 51 h and 69 h
after the first game and immediately after the second game. Blood samples were
taken 3 h before, immediately after (within 15-20 min), 21 h, 45 h, 69 h after the
first game and immediately after the second game (Fig 1). Two days before the
commencement of the study, all subjects performed a maximal oxygen consumption
24 I The physiological impact of soccer on elite... ✍ helena andersson
24
running test on a treadmill. One day before the start of the study, the players were
familiarised with all testing procedures.
Figure 1. Schematic view of the study set-up. indicates performance parameter tests;
indicates blood sampling.
The study was designed to mirror an actual competitive situation for female
players participating in an international tournament, where two days of recovery
between the games are allowed. The total time for the study period was seven days
including travelling. In order to standardise the physical activity and nutritional
intake during the study period the players stayed in the same hotel and ate every
meal together. The games were conducted in the middle of the season (during the
summer break) when the players were accustomed to high training and game loads.
The first game in the study was played four days after the last game in the domestic
leagues. Therefore, all players had rested at least three days from games and two
days from soccer training prior to the first game.
3.3 ACTIVE RECOVERY TRAINING
The active recovery training consisted of a low-intensity training program lasting one
hour. The training consisted of 20 min sub-maximal cycling (60% of HFpeak,
approximately 45% of 2
•
VO peak) and 30 min low-intensity resistance training
(<50% 1 RM), and 10 min sub-maximal cycling (60% of HFpeak) (Fig. 2). The low-
intensity resistance training included exercises for both the upper and lower body.
The exercise intensity during the cycling was monitored using a heart-rate monitor
25
(S610i, Polar Electro OY, Kempele, Finland). The rationale for using cycling as the
low-aerobic training was that it increases blood flow in the leg muscles whilst
minimising the load on the muscles which is proposed to be beneficial for recovery
(Reilly & Ekblom 2005). The performance of low-intensity resistance weight
training may enhance the protein metabolism in the exercised muscle, which would
also be beneficial for recovery. The session was designed to mirror the recovery
training used by many Nordic soccer teams. During the active recovery sessions the
subjects drank 1 L of a sports drink that provided a carbohydrate load of 30-60 g
per hour. During the one-hour period when the active recovery group performed the
low-intensity exercise, the control group was instructed to rest.
Figure 2. Participants performing the active recovery training.
3.4 DIET
The food intake was standardised for all players during the study period, starting on
the evening before the first game. All players were given a meal plan formulated by a
nutritionist and the players ate each meal together. The composition of the meals
was developed using a national food database ("Food on data" 4.3 LKH, Norway).
Intake of carbohydrate (CHO), protein and fat were adjusted to each player’s body
weight (55/60/65/70 kg respectively) to meet the recommendations for daily recovery
in players participating in moderate training (intake of ≥ 6 g/kg body mass CHO,
and ≥ 1.2 g/kg body mass protein) (Maughan et al. 2004). The food was chosen to
replicate the player’s normal diet as much as possible and did not contain any food
items with known high-antioxidant levels. The meal plan included a variation of
bread, cereals, milk/yoghurts, meat, pasta/rice, fruit and vegetables to ensure
The physiological impact of soccer on elite... ✍ helena andersson I 25
24
running test on a treadmill. One day before the start of the study, the players were
familiarised with all testing procedures.
Figure 1. Schematic view of the study set-up. indicates performance parameter tests;
indicates blood sampling.
The study was designed to mirror an actual competitive situation for female
players participating in an international tournament, where two days of recovery
between the games are allowed. The total time for the study period was seven days
including travelling. In order to standardise the physical activity and nutritional
intake during the study period the players stayed in the same hotel and ate every
meal together. The games were conducted in the middle of the season (during the
summer break) when the players were accustomed to high training and game loads.
The first game in the study was played four days after the last game in the domestic
leagues. Therefore, all players had rested at least three days from games and two
days from soccer training prior to the first game.
3.3 ACTIVE RECOVERY TRAINING
The active recovery training consisted of a low-intensity training program lasting one
hour. The training consisted of 20 min sub-maximal cycling (60% of HFpeak,
approximately 45% of 2
•
VO peak) and 30 min low-intensity resistance training
(<50% 1 RM), and 10 min sub-maximal cycling (60% of HFpeak) (Fig. 2). The low-
intensity resistance training included exercises for both the upper and lower body.
The exercise intensity during the cycling was monitored using a heart-rate monitor
25
(S610i, Polar Electro OY, Kempele, Finland). The rationale for using cycling as the
low-aerobic training was that it increases blood flow in the leg muscles whilst
minimising the load on the muscles which is proposed to be beneficial for recovery
(Reilly & Ekblom 2005). The performance of low-intensity resistance weight
training may enhance the protein metabolism in the exercised muscle, which would
also be beneficial for recovery. The session was designed to mirror the recovery
training used by many Nordic soccer teams. During the active recovery sessions the
subjects drank 1 L of a sports drink that provided a carbohydrate load of 30-60 g
per hour. During the one-hour period when the active recovery group performed the
low-intensity exercise, the control group was instructed to rest.
Figure 2. Participants performing the active recovery training.
3.4 DIET
The food intake was standardised for all players during the study period, starting on
the evening before the first game. All players were given a meal plan formulated by a
nutritionist and the players ate each meal together. The composition of the meals
was developed using a national food database ("Food on data" 4.3 LKH, Norway).
Intake of carbohydrate (CHO), protein and fat were adjusted to each player’s body
weight (55/60/65/70 kg respectively) to meet the recommendations for daily recovery
in players participating in moderate training (intake of ≥ 6 g/kg body mass CHO,
and ≥ 1.2 g/kg body mass protein) (Maughan et al. 2004). The food was chosen to
replicate the player’s normal diet as much as possible and did not contain any food
items with known high-antioxidant levels. The meal plan included a variation of
bread, cereals, milk/yoghurts, meat, pasta/rice, fruit and vegetables to ensure
26 I The physiological impact of soccer on elite... ✍ helena andersson
26
adequate intake of macro- and micronutrients. In addition, the players were
instructed to drink a sports drink during the games providing approximately 30-60g
CHO/h (Maxim EnergyTM, Ishøj, Denmark). The sports drink did not contain
vitamin C. After the blood sample was taken at the end of each game, each player
consumed a CHO intake of 1 g/kg body weight within 30 min to ensure optimal
recovery (banana, yoghurt, and sports drink) (Maughan et al. 2004).
3.5 EVALUATION OF WORKLOAD DURING THE GAMES
In order to compare the workload of the games, each player’s heart rate was
recorded during the games. The players wore heart-rate monitors around their chests
(Polar Team System, Polar Electro OY, Kempele, Finland) and data were
continuously collected every 5 s. In addition to heart-rate measurements the players’
movement pattern and fluid loss were also recorded during the games. The
movement pattern, including total distance covered and distance covered in high-
intensity running (HIR) was collected from a total of ten players who played in
different field positions (four defenders, three midfielders and three forwards). These
ten players gave a representation of the movement pattern during the games. Each of
these ten players was filmed in close-up by a digital camera (Canon DM-MV 600,
Canon Inc., Tokyo, Japan) during the entire first and second games. The cameras
were positioned at the side of the field, at the level of the midfield line, at a height of
about 15 m above the field and at a distance of 30-40 m from the side line. The
videotapes were later replayed on a monitor for computerized coding of the activity
pattern. The locomotor speed ranges for high-intensity running were chosen
according to Krustrup et al., (2005). These speeds were: moderate-speed running
(15-17 km·h-1), high-speed running (18-24 km·h-1) and sprinting (> 25 km·h-1). The
distance covered for each activity within each interval was determined as the product
of the total time and mean speed for that activity. All game recordings were analysed
by the same experienced observer with a coefficient of variation (CV) for test-retest
analysis of <3% for total distance covered and <5% for distance covered in high-
intensity running.
The players‘ body mass was measured before and immediately after the games
using a digital scale (Seca 708, Seca Ltd, Birmingham, United Kingdom). The
27
players’ fluid intake was recorded during the games and the total fluid loss was
calculated by the formula: Fluid loss = ∆ Body Weight + fluid intake.
3.6 BLOOD SAMPLING
First in the testing procedure, blood was collected from an antecubital vein into 4-ml
EDTA vacutainers and a 9 ml vacutainer tube. The blood in the 9-ml vacutainer tube
coagulated at room temperature for 30-45 min. Serum was pipetted off and stored in
Eppendorf tubes at -80 °C until analysis. One of the EDTA tubes was centrifuged at
1500 g at 4 °C for 15 min to get the required plasma. Plasma was further centrifuged
for 5 min at 11 000 g at 4 °C; the supernatant was stored at – 80 °C until analysis.
3.7 NEUROMUSCULAR FATIGUE AND BLOOD MARKERS OF PHYSICAL
STRESS
3.7.13.7.13.7.13.7.1 SSSSprint, CMJ and isokinetic strength testsprint, CMJ and isokinetic strength testsprint, CMJ and isokinetic strength testsprint, CMJ and isokinetic strength tests
Prior to the sprint, CMJ and isokinetic knee strength tests, the players performed a
standardised warm-up consisting of five min low-intensity running (using the YOYO
intermittent endurance test level 1) (Krustrup et al. 2003). After the warm-up the
players performed three maximal 20-m sprints: the best result was used in the data
analysis. The players were instructed to stand with one foot on a marker and the
time was started when the subjects touched a mechanical switch (placed 88 cm from
the marker) in the first step. Sprint time was thereafter measured with photocells
every 10-m (CV<1%). The photocells were placed at a height of 133 cm.
CMJ was performed on a force plate (SG 9, Advanced Mechanical Technology Inc.,
Newton, MA, USA) and low-pass filtered at 1050 Hz. The CMJ started from a
standing position with the hands fixed to the hips. Jump-height was calculated from
the vertical reaction force impulse during take-off. At each test the players performed
three jumps with the best used in the data analysis (CV<5%).
Isokinetic concentric knee extensions and flexions (Fig. 3) were performed using
two instruments, the Cybex 6000 dynamometer (Lumex, Ronkonfoma, NY, USA)
The physiological impact of soccer on elite... ✍ helena andersson I 27
26
adequate intake of macro- and micronutrients. In addition, the players were
instructed to drink a sports drink during the games providing approximately 30-60g
CHO/h (Maxim EnergyTM, Ishøj, Denmark). The sports drink did not contain
vitamin C. After the blood sample was taken at the end of each game, each player
consumed a CHO intake of 1 g/kg body weight within 30 min to ensure optimal
recovery (banana, yoghurt, and sports drink) (Maughan et al. 2004).
3.5 EVALUATION OF WORKLOAD DURING THE GAMES
In order to compare the workload of the games, each player’s heart rate was
recorded during the games. The players wore heart-rate monitors around their chests
(Polar Team System, Polar Electro OY, Kempele, Finland) and data were
continuously collected every 5 s. In addition to heart-rate measurements the players’
movement pattern and fluid loss were also recorded during the games. The
movement pattern, including total distance covered and distance covered in high-
intensity running (HIR) was collected from a total of ten players who played in
different field positions (four defenders, three midfielders and three forwards). These
ten players gave a representation of the movement pattern during the games. Each of
these ten players was filmed in close-up by a digital camera (Canon DM-MV 600,
Canon Inc., Tokyo, Japan) during the entire first and second games. The cameras
were positioned at the side of the field, at the level of the midfield line, at a height of
about 15 m above the field and at a distance of 30-40 m from the side line. The
videotapes were later replayed on a monitor for computerized coding of the activity
pattern. The locomotor speed ranges for high-intensity running were chosen
according to Krustrup et al., (2005). These speeds were: moderate-speed running
(15-17 km·h-1), high-speed running (18-24 km·h-1) and sprinting (> 25 km·h-1). The
distance covered for each activity within each interval was determined as the product
of the total time and mean speed for that activity. All game recordings were analysed
by the same experienced observer with a coefficient of variation (CV) for test-retest
analysis of <3% for total distance covered and <5% for distance covered in high-
intensity running.
The players‘ body mass was measured before and immediately after the games
using a digital scale (Seca 708, Seca Ltd, Birmingham, United Kingdom). The
27
players’ fluid intake was recorded during the games and the total fluid loss was
calculated by the formula: Fluid loss = ∆ Body Weight + fluid intake.
3.6 BLOOD SAMPLING
First in the testing procedure, blood was collected from an antecubital vein into 4-ml
EDTA vacutainers and a 9 ml vacutainer tube. The blood in the 9-ml vacutainer tube
coagulated at room temperature for 30-45 min. Serum was pipetted off and stored in
Eppendorf tubes at -80 °C until analysis. One of the EDTA tubes was centrifuged at
1500 g at 4 °C for 15 min to get the required plasma. Plasma was further centrifuged
for 5 min at 11 000 g at 4 °C; the supernatant was stored at – 80 °C until analysis.
3.7 NEUROMUSCULAR FATIGUE AND BLOOD MARKERS OF PHYSICAL
STRESS
3.7.13.7.13.7.13.7.1 SSSSprint, CMJ and isokinetic strength testsprint, CMJ and isokinetic strength testsprint, CMJ and isokinetic strength testsprint, CMJ and isokinetic strength tests
Prior to the sprint, CMJ and isokinetic knee strength tests, the players performed a
standardised warm-up consisting of five min low-intensity running (using the YOYO
intermittent endurance test level 1) (Krustrup et al. 2003). After the warm-up the
players performed three maximal 20-m sprints: the best result was used in the data
analysis. The players were instructed to stand with one foot on a marker and the
time was started when the subjects touched a mechanical switch (placed 88 cm from
the marker) in the first step. Sprint time was thereafter measured with photocells
every 10-m (CV<1%). The photocells were placed at a height of 133 cm.
CMJ was performed on a force plate (SG 9, Advanced Mechanical Technology Inc.,
Newton, MA, USA) and low-pass filtered at 1050 Hz. The CMJ started from a
standing position with the hands fixed to the hips. Jump-height was calculated from
the vertical reaction force impulse during take-off. At each test the players performed
three jumps with the best used in the data analysis (CV<5%).
Isokinetic concentric knee extensions and flexions (Fig. 3) were performed using
two instruments, the Cybex 6000 dynamometer (Lumex, Ronkonfoma, NY, USA)
28 I The physiological impact of soccer on elite... ✍ helena andersson
28
and the Technogym REV 9000 (Gambettola, Italy). This combination of equipment
was chosen in order to enable testing of all subjects to be completed in the shortest
possible period of time. Although controlled studies revealed that there were no
differences in performance measured using the two instruments, the same subject
was always tested on the same machine. The range of motion was set from a knee
angle of 90° to 20° from full extension and the angular velocity of contraction of the
isokinetic dynamometer rotating lever arm was set at 60°·s-1. The subjects performed
four warm-up contractions followed by three maximal contractions. Peak torque
was analysed (CV<5%) and one leg was tested (dominant leg). The tight testing time
schedule prevented isokinetic maximal strength at 45 h and sprint performance at 51
h after the first game from being measured.
Figure 3. A player performing the isokinetic knee-strength test.
3.7.23.7.23.7.23.7.2 Perceived muscle soreness Perceived muscle soreness Perceived muscle soreness Perceived muscle soreness
Perceived muscle soreness was assessed using a 7-point Likert scale (Morgan et al.
1988). It is designed to measure the level of muscle soreness in the lower body. The
scale consisted of the following verbal anchors: 1 = very, very good; 2 = very good; 3
= good; 4 = tender but not sore; 5 = sore; 6 = very sore; and 7 = very, very sore.
Scores were recorded to the nearest 0.5 decimal point.
29
3.7.33.7.33.7.33.7.3 Blood marBlood marBlood marBlood markers of physical stress; CK, urea, uric acid and glucosekers of physical stress; CK, urea, uric acid and glucosekers of physical stress; CK, urea, uric acid and glucosekers of physical stress; CK, urea, uric acid and glucose
CK, urea, uric acid and glucose were measured in plasma and were analysed with
standard routine measurements in a Modular P® Analyzer (Hitachi, Tokyo, Japan).
CVs for all variables were <5%.
3.8 OXIDATIVE STRESS MARKERS AND ANTIOXIDANT COMPOUNDS
3.8.13.8.13.8.13.8.1 Oxidative stress markersOxidative stress markersOxidative stress markersOxidative stress markers
The Diacrons reactive oxygen metabolites (d-ROMs) test was used to assess lipid
peroxidation and was performed according to the manufacturer’s instructions
(Diacron International, Grossetto, Italy). The analysis was fully automated, using a
Technicon RA 1000 system (Technicon Instruments Corporation, NY, USA). The d-
ROMs test monitors a rather persistent radical cation formed in the reaction of
alkoxy and peroxy radicals derived from the hydroperoxides with a suitable additive
N, N, diethyl-para-phenylendiamine (DEPPD). Thus, the d-ROMs level is
proportional to the serum hydroperoxide concentration in plasma (Alberti et al.
2000). Hydroperoxides are products of the peroxidation of proteins, peptides, amino
acids, lipids, and fatty acids (Nakayama et al. 2007). The test was carried out in the
kinetic mode. Results are expressed in arbitrary units (CARR Units) (Cesarone et al.
1999) with a CV <10%. According to the manufacturer’s instructions a normal
value for d-ROMs is between 250 and 300 CARR U in healthy individuals. In
trained individuals lower basal values have been reported (< 250 CARR U) (Banfi et
al. 2006). A value between 301 and 320 CARR U indicates a borderline condition of
oxidative stress status, while a value above 320 CARR U indicates oxidative stress
(Diacron International, Grossetto, Italy).
Quantification of oxidized glutathione (GSSG) and reduced glutathione (GSH)
was performed using a two-dimensional chromatographic system with parallel
Hypercarb columns coupled with dual fluorescence detectors (FLD). After sample
preparation as previously described (Sakhi et al. 2006), 10 μL of the supernatant was
injected into the chromatographic system. Derivatisation of GSSG was performed
using monobromobimane (MBB) and ortho-phthalaldehyde (OPA). The CV for the
method was below 7%. The ratio of GSH:GSSG was calculated by dividing GSH
with GSSG. We analysed glutathione in plasma. In comparison to whole blood
The physiological impact of soccer on elite... ✍ helena andersson I 29
28
and the Technogym REV 9000 (Gambettola, Italy). This combination of equipment
was chosen in order to enable testing of all subjects to be completed in the shortest
possible period of time. Although controlled studies revealed that there were no
differences in performance measured using the two instruments, the same subject
was always tested on the same machine. The range of motion was set from a knee
angle of 90° to 20° from full extension and the angular velocity of contraction of the
isokinetic dynamometer rotating lever arm was set at 60°·s-1. The subjects performed
four warm-up contractions followed by three maximal contractions. Peak torque
was analysed (CV<5%) and one leg was tested (dominant leg). The tight testing time
schedule prevented isokinetic maximal strength at 45 h and sprint performance at 51
h after the first game from being measured.
Figure 3. A player performing the isokinetic knee-strength test.
3.7.23.7.23.7.23.7.2 Perceived muscle soreness Perceived muscle soreness Perceived muscle soreness Perceived muscle soreness
Perceived muscle soreness was assessed using a 7-point Likert scale (Morgan et al.
1988). It is designed to measure the level of muscle soreness in the lower body. The
scale consisted of the following verbal anchors: 1 = very, very good; 2 = very good; 3
= good; 4 = tender but not sore; 5 = sore; 6 = very sore; and 7 = very, very sore.
Scores were recorded to the nearest 0.5 decimal point.
29
3.7.33.7.33.7.33.7.3 Blood marBlood marBlood marBlood markers of physical stress; CK, urea, uric acid and glucosekers of physical stress; CK, urea, uric acid and glucosekers of physical stress; CK, urea, uric acid and glucosekers of physical stress; CK, urea, uric acid and glucose
CK, urea, uric acid and glucose were measured in plasma and were analysed with
standard routine measurements in a Modular P® Analyzer (Hitachi, Tokyo, Japan).
CVs for all variables were <5%.
3.8 OXIDATIVE STRESS MARKERS AND ANTIOXIDANT COMPOUNDS
3.8.13.8.13.8.13.8.1 Oxidative stress markersOxidative stress markersOxidative stress markersOxidative stress markers
The Diacrons reactive oxygen metabolites (d-ROMs) test was used to assess lipid
peroxidation and was performed according to the manufacturer’s instructions
(Diacron International, Grossetto, Italy). The analysis was fully automated, using a
Technicon RA 1000 system (Technicon Instruments Corporation, NY, USA). The d-
ROMs test monitors a rather persistent radical cation formed in the reaction of
alkoxy and peroxy radicals derived from the hydroperoxides with a suitable additive
N, N, diethyl-para-phenylendiamine (DEPPD). Thus, the d-ROMs level is
proportional to the serum hydroperoxide concentration in plasma (Alberti et al.
2000). Hydroperoxides are products of the peroxidation of proteins, peptides, amino
acids, lipids, and fatty acids (Nakayama et al. 2007). The test was carried out in the
kinetic mode. Results are expressed in arbitrary units (CARR Units) (Cesarone et al.
1999) with a CV <10%. According to the manufacturer’s instructions a normal
value for d-ROMs is between 250 and 300 CARR U in healthy individuals. In
trained individuals lower basal values have been reported (< 250 CARR U) (Banfi et
al. 2006). A value between 301 and 320 CARR U indicates a borderline condition of
oxidative stress status, while a value above 320 CARR U indicates oxidative stress
(Diacron International, Grossetto, Italy).
Quantification of oxidized glutathione (GSSG) and reduced glutathione (GSH)
was performed using a two-dimensional chromatographic system with parallel
Hypercarb columns coupled with dual fluorescence detectors (FLD). After sample
preparation as previously described (Sakhi et al. 2006), 10 μL of the supernatant was
injected into the chromatographic system. Derivatisation of GSSG was performed
using monobromobimane (MBB) and ortho-phthalaldehyde (OPA). The CV for the
method was below 7%. The ratio of GSH:GSSG was calculated by dividing GSH
with GSSG. We analysed glutathione in plasma. In comparison to whole blood
30 I The physiological impact of soccer on elite... ✍ helena andersson
30
glutathione, plasma contains less than 1% glutathione (Ji 2000). Plasma glutathione
can, however, be used as a model for intracellular glutathione, as it is assumed that
plasma glutathione reflects intracellular whole blood glutathione. Reduced plasma
glutathione (GSH) constitutes about 50-70% of total plasma glutathione while
GSSG constitutes about 5-10% of GSH. Moreover, the fraction of TGSH in our
study includes other components other than pure glutathione, such as adducts of
plasma proteins, while GSH and GSSG are free plasma glutathione. Hence, the
observed value of TGSH is higher compared to GSH and GSSG.
3.8.23.8.23.8.23.8.2 Antioxidant compounds Antioxidant compounds Antioxidant compounds Antioxidant compounds
For the determination of the dietary antioxidant ascorbic acid, heparin plasma was
immediately acidified using an equal volume of 10% meta-phoshoric acid (MPA)
and stored at -70 °C until analysis within 3 months. Samples were analysed by high
performance liquid chromatography (HPLC) (Karlsen et al. 2005, 2007) with a CV
below 5%. Plasma calibrators quantified against the NIST 970 SRM served as
standards.
For the determination of the tocopherols by HPLC, proteins were precipitated by
the addition of 3 volumes of isopropanol, followed by centrifugation at 3000 g at 4
°C for 15 min. The internal standard tocol was added with the isopropanol and 5 µL
of the clear supernatant were used for analysis (Richheimer et al. 1994). A
fluorescence detector operated at 295 nm (ex) and 330 nm (em) was used for
detection with a CV below 5%. Standards prepared in 1% bovine serum albumin in
phosphate buffered saline were used for quantification. Total tocoperhols is the sum
of -, -, -, and – tocopherols.
For analysis of the dietary antioxidants total polyphenols, 50 µL heparin plasma
were mixed with 150 µL ethanol for 2 min, before centrifugation at 3000 g at 4 °C
for 15 min. Fifty microliters of the clear supernatant were used for the Folin-
Ciocalteu method as previously described (Maskarinec et al. 1999). Quercetin
prepared in ethanol served as standard solution, and the results are given as µmol/L
quercetin equivalents (QE) with a CV below 10%.
The total carotenoids is the sum of lutein, zeaxanthin, β-krytpoxanthin, α-
carotene, β-carotene and lycopene. These dietary antioxidants were determined in
plasma by HPLC. Proteins were precipitated and removed by the addition of a 4.5
volume of isopropanol followed by centrifugation at 3000 g at 4 °C for 15 min. The
internal standard astaxanthin was added in the isopropanol. Twenty-five microliters
31
of the clear supernatant were used for analysis. The mobile phases consisted of A:
20% water and 24% acetone in ethanol and B: acetone. The gradient conditions
were as follows: from 2 to 100% B within 20 min, followed by 100% B for 15 min.
Detection was performed at 453 nm using a variable wavelength detector. Plasma
calibrators quantified against the NIST 968c SRM were used as standards and the
CV for the method was below 5%.
The non-enzymatic endogenous antioxidants thiols (including total glutathione
(TGSH), cysteine, homocysteine and cysteine-glycine) were analysed in plasma with
the use of chemical reduction and according the “homocysteine by HPLC” kit
provided by Biorad Laboratories GmbH (Munich, Germany). Standard solutions
prepared in PBS served as calibrators with a CV <5%. Ferric reducing/antioxidant
power assay (FRAP) was determined in plasma as described elsewhere (Benzie &
Strain 1999).
3.9 INFLAMMATORY CELLS AND CYTOKINE RESPONSE
3.9.13.9.13.9.13.9.1 Leukocyte Leukocyte Leukocyte Leukocyte cellcellcellcell count count count count
Leukocyte cell numbers were analysed with a Sysmex K-1000 (TOA Medical
Electronics Co., Ltd., Kobe, Japan). Coefficient of variation for neutrophil and
lymphocyte cell counts are <4%. Leukocytes in EDTA whole blood were counted as
total number of leukocytes (white blood cells), neutrophils, lymphocytes and mixed
cells. Mixed cells are monocytes, basophils, eosinophils and granolucytes.
3.9.23.9.23.9.23.9.2 Cytokine analysCytokine analysCytokine analysCytokine analysiiiissss
IL-1, IL-1Ra, IL-2, IL -2R, IL-4, IL-5, IL-6, IL-7, INF-, INF-α, IL-8, IL-10, IL-12,
IL-13, IL-15, IL-17, TNF-α, GM-CSF, IP-10, MIP-1α,β, MCP-1, MIG, Eotaxin and
RANTES were measured in plasma by a validated sandwich immunoassay based
protein array system commercial kit (Biosource International, kit no. LHC009,
Camarillo, CA, USA). Cytokine detection was performed according to the
manufacturer's instruction, with assay diluents as blank. Calibration standards were
prepared in the assay buffer. In brief: antibody-coupled microspheres specific for the
different cytokines were incubated with plasma. Antigen binding was then detected
after incubation with biotinylated detector antibodies. Detection was performed with
The physiological impact of soccer on elite... ✍ helena andersson I 31
30
glutathione, plasma contains less than 1% glutathione (Ji 2000). Plasma glutathione
can, however, be used as a model for intracellular glutathione, as it is assumed that
plasma glutathione reflects intracellular whole blood glutathione. Reduced plasma
glutathione (GSH) constitutes about 50-70% of total plasma glutathione while
GSSG constitutes about 5-10% of GSH. Moreover, the fraction of TGSH in our
study includes other components other than pure glutathione, such as adducts of
plasma proteins, while GSH and GSSG are free plasma glutathione. Hence, the
observed value of TGSH is higher compared to GSH and GSSG.
3.8.23.8.23.8.23.8.2 Antioxidant compounds Antioxidant compounds Antioxidant compounds Antioxidant compounds
For the determination of the dietary antioxidant ascorbic acid, heparin plasma was
immediately acidified using an equal volume of 10% meta-phoshoric acid (MPA)
and stored at -70 °C until analysis within 3 months. Samples were analysed by high
performance liquid chromatography (HPLC) (Karlsen et al. 2005, 2007) with a CV
below 5%. Plasma calibrators quantified against the NIST 970 SRM served as
standards.
For the determination of the tocopherols by HPLC, proteins were precipitated by
the addition of 3 volumes of isopropanol, followed by centrifugation at 3000 g at 4
°C for 15 min. The internal standard tocol was added with the isopropanol and 5 µL
of the clear supernatant were used for analysis (Richheimer et al. 1994). A
fluorescence detector operated at 295 nm (ex) and 330 nm (em) was used for
detection with a CV below 5%. Standards prepared in 1% bovine serum albumin in
phosphate buffered saline were used for quantification. Total tocoperhols is the sum
of -, -, -, and – tocopherols.
For analysis of the dietary antioxidants total polyphenols, 50 µL heparin plasma
were mixed with 150 µL ethanol for 2 min, before centrifugation at 3000 g at 4 °C
for 15 min. Fifty microliters of the clear supernatant were used for the Folin-
Ciocalteu method as previously described (Maskarinec et al. 1999). Quercetin
prepared in ethanol served as standard solution, and the results are given as µmol/L
quercetin equivalents (QE) with a CV below 10%.
The total carotenoids is the sum of lutein, zeaxanthin, β-krytpoxanthin, α-
carotene, β-carotene and lycopene. These dietary antioxidants were determined in
plasma by HPLC. Proteins were precipitated and removed by the addition of a 4.5
volume of isopropanol followed by centrifugation at 3000 g at 4 °C for 15 min. The
internal standard astaxanthin was added in the isopropanol. Twenty-five microliters
31
of the clear supernatant were used for analysis. The mobile phases consisted of A:
20% water and 24% acetone in ethanol and B: acetone. The gradient conditions
were as follows: from 2 to 100% B within 20 min, followed by 100% B for 15 min.
Detection was performed at 453 nm using a variable wavelength detector. Plasma
calibrators quantified against the NIST 968c SRM were used as standards and the
CV for the method was below 5%.
The non-enzymatic endogenous antioxidants thiols (including total glutathione
(TGSH), cysteine, homocysteine and cysteine-glycine) were analysed in plasma with
the use of chemical reduction and according the “homocysteine by HPLC” kit
provided by Biorad Laboratories GmbH (Munich, Germany). Standard solutions
prepared in PBS served as calibrators with a CV <5%. Ferric reducing/antioxidant
power assay (FRAP) was determined in plasma as described elsewhere (Benzie &
Strain 1999).
3.9 INFLAMMATORY CELLS AND CYTOKINE RESPONSE
3.9.13.9.13.9.13.9.1 Leukocyte Leukocyte Leukocyte Leukocyte cellcellcellcell count count count count
Leukocyte cell numbers were analysed with a Sysmex K-1000 (TOA Medical
Electronics Co., Ltd., Kobe, Japan). Coefficient of variation for neutrophil and
lymphocyte cell counts are <4%. Leukocytes in EDTA whole blood were counted as
total number of leukocytes (white blood cells), neutrophils, lymphocytes and mixed
cells. Mixed cells are monocytes, basophils, eosinophils and granolucytes.
3.9.23.9.23.9.23.9.2 Cytokine analysCytokine analysCytokine analysCytokine analysiiiissss
IL-1, IL-1Ra, IL-2, IL -2R, IL-4, IL-5, IL-6, IL-7, INF-, INF-α, IL-8, IL-10, IL-12,
IL-13, IL-15, IL-17, TNF-α, GM-CSF, IP-10, MIP-1α,β, MCP-1, MIG, Eotaxin and
RANTES were measured in plasma by a validated sandwich immunoassay based
protein array system commercial kit (Biosource International, kit no. LHC009,
Camarillo, CA, USA). Cytokine detection was performed according to the
manufacturer's instruction, with assay diluents as blank. Calibration standards were
prepared in the assay buffer. In brief: antibody-coupled microspheres specific for the
different cytokines were incubated with plasma. Antigen binding was then detected
after incubation with biotinylated detector antibodies. Detection was performed with
32 I The physiological impact of soccer on elite... ✍ helena andersson
32
the use of a flow-based dual laser detector with real-time digital signal. The Luminex
100 IS instrument (Biosource, Nivelles, Belgium) with the Star Station acquisition
program (v2 Applied Cytometry Systems, Sheffield, UK) were used to process the
data. According to the manufacturer, both intra-assay variations and inter-assay
variations for all antigens measured by the multiplex system are below 10%.
Furthermore, the sensitivity of multiplex Bead Array assays for the detection of
soluble cytokines from various manufacturers has been compared (Khan et al. 2004).
First, Bead Array and ELISA values appeared to be comparable between the
manufacturers (Khan et al. 2004). Second, the minimal detection range for the kit
used in our study (Biosource kit) was comparable and even several-fold higher than
that of other kits (Khan et al. 2004). Third, the sensitivity limits are equivalent to
those of most ELISA’s (Martins et al. 2002). All samples were run in double samples
according to the manufacturer's recommendations.
3.10 STATISTICAL ANALYSES
Data are presented as means and standard deviation (SD), or standard error of the
mean (SE). All data were tested for their normal distribution prior to statistical
calculations. The statistical significance of the differences between groups and time
points was determined using a two-way (group x time) repeated-measures ANOVA
using absolute values. Where appropriate, Dunnett’s post hoc test and Tukey’s post
hoc test were applied. In addition to describing the changes that occurred from
baseline values, we also analysed the gradient of change from immediately before
and after the first and second games (Study I, III, IV). In study II, the d-ROMs data
were not normally distributed and were log-10 transformed prior to ANOVA. In
study III, not normally distributed data were analysed using Friedman’s non-
parametric related samples test with a Dunn’s post hoc test. Selected bivariate
relationships were examined with the Pearson’s product-moment correlation
coefficient test for normally distributed data, whereas the Spearman rank correlation
coefficient test was used to analyse data that did not meet the assumption of
normality. P values below 0.05 were considered statistically significant. The
Statistical Package for the Social Sciences (SPSS Inc, version 12.0) and Statistica
(StatSoft Inc, version 7.0) were used for the analyses.
33
3.11 ETHICAL APPROVAL
The players were informed of the experimental procedures and possible discomforts
associated with the study and gave their written informed consent to participate. The
study was conducted according to the policy statement set forth in the Declaration of
Helsinki and approved by the Regional Ethics Committee of Uppsala, Sweden (Dnr
2004: M-364).
The physiological impact of soccer on elite... ✍ helena andersson I 33
32
the use of a flow-based dual laser detector with real-time digital signal. The Luminex
100 IS instrument (Biosource, Nivelles, Belgium) with the Star Station acquisition
program (v2 Applied Cytometry Systems, Sheffield, UK) were used to process the
data. According to the manufacturer, both intra-assay variations and inter-assay
variations for all antigens measured by the multiplex system are below 10%.
Furthermore, the sensitivity of multiplex Bead Array assays for the detection of
soluble cytokines from various manufacturers has been compared (Khan et al. 2004).
First, Bead Array and ELISA values appeared to be comparable between the
manufacturers (Khan et al. 2004). Second, the minimal detection range for the kit
used in our study (Biosource kit) was comparable and even several-fold higher than
that of other kits (Khan et al. 2004). Third, the sensitivity limits are equivalent to
those of most ELISA’s (Martins et al. 2002). All samples were run in double samples
according to the manufacturer's recommendations.
3.10 STATISTICAL ANALYSES
Data are presented as means and standard deviation (SD), or standard error of the
mean (SE). All data were tested for their normal distribution prior to statistical
calculations. The statistical significance of the differences between groups and time
points was determined using a two-way (group x time) repeated-measures ANOVA
using absolute values. Where appropriate, Dunnett’s post hoc test and Tukey’s post
hoc test were applied. In addition to describing the changes that occurred from
baseline values, we also analysed the gradient of change from immediately before
and after the first and second games (Study I, III, IV). In study II, the d-ROMs data
were not normally distributed and were log-10 transformed prior to ANOVA. In
study III, not normally distributed data were analysed using Friedman’s non-
parametric related samples test with a Dunn’s post hoc test. Selected bivariate
relationships were examined with the Pearson’s product-moment correlation
coefficient test for normally distributed data, whereas the Spearman rank correlation
coefficient test was used to analyse data that did not meet the assumption of
normality. P values below 0.05 were considered statistically significant. The
Statistical Package for the Social Sciences (SPSS Inc, version 12.0) and Statistica
(StatSoft Inc, version 7.0) were used for the analyses.
33
3.11 ETHICAL APPROVAL
The players were informed of the experimental procedures and possible discomforts
associated with the study and gave their written informed consent to participate. The
study was conducted according to the policy statement set forth in the Declaration of
Helsinki and approved by the Regional Ethics Committee of Uppsala, Sweden (Dnr
2004: M-364).
34 35
4 RESULTS AND DISCUSSION
4.1 WORKLOAD DURING THE GAMES
4.1.14.1.14.1.14.1.1 Main findings Main findings Main findings Main findings
Heart rate. No significant differences were observed in heart-rate values between the
active recovery and passive groups during the games. The mean heart rate was
relatively high in both games (> 160 bpm). The HR ranged between 144–173 bpm in
the first game and 152-180 bpm in the second game, showing individual differences.
The mean heart rate and time spent above 85% and 90% of HRpeak were slightly,
but significantly, higher during the second game (Table 1).
Table 1. Heart rate in beats.min-1, % HRpeak and time spent above 85% and 90%
of HRpeak during the games for the active recovery and passive groups.
Game 1 Game 2
Active group (n=8) 1st
half 2nd
half Total game 1st
half 2nd
half Total game
HR (beats.min
-1)
165±3
162±3
163±3
173±3 *
169±3 *
171±3 *
% of HRpeak (%)
83±1
82±1
82±1
87±1*
85±1*
86±1*
> 85% HRpeak (min)
23±3
18±3
41±6
29±5
28±3
57±5*
> 90% HRpeak (min)
9±3
6±2
15±5
14±4
10±3*
24±4*
Passive group (n=9) HR (beats.min
-1)
162±2
160±2
161±2
172±3 *
165±2 *
168±2 *
% of HRpeak (%)
82±1
81±1
81±1
86±1*
83±1*
85±1*
> 85% HRpeak (min)
22±2
17±3
38±5
26±5
23±3
49±6*
> 90% HRpeak (min)
9±2
5±2
14±4
15±4
8±2*
23±5*
Values are in means ± SE. * denotes significantly higher (p<0.05) compared to the
first game.
The physiological impact of soccer on elite... ✍ helena andersson I 35
34 35
4 RESULTS AND DISCUSSION
4.1 WORKLOAD DURING THE GAMES
4.1.14.1.14.1.14.1.1 Main findings Main findings Main findings Main findings
Heart rate. No significant differences were observed in heart-rate values between the
active recovery and passive groups during the games. The mean heart rate was
relatively high in both games (> 160 bpm). The HR ranged between 144–173 bpm in
the first game and 152-180 bpm in the second game, showing individual differences.
The mean heart rate and time spent above 85% and 90% of HRpeak were slightly,
but significantly, higher during the second game (Table 1).
Table 1. Heart rate in beats.min-1, % HRpeak and time spent above 85% and 90%
of HRpeak during the games for the active recovery and passive groups.
Game 1 Game 2
Active group (n=8) 1st
half 2nd
half Total game 1st
half 2nd
half Total game
HR (beats.min
-1)
165±3
162±3
163±3
173±3 *
169±3 *
171±3 *
% of HRpeak (%)
83±1
82±1
82±1
87±1*
85±1*
86±1*
> 85% HRpeak (min)
23±3
18±3
41±6
29±5
28±3
57±5*
> 90% HRpeak (min)
9±3
6±2
15±5
14±4
10±3*
24±4*
Passive group (n=9) HR (beats.min
-1)
162±2
160±2
161±2
172±3 *
165±2 *
168±2 *
% of HRpeak (%)
82±1
81±1
81±1
86±1*
83±1*
85±1*
> 85% HRpeak (min)
22±2
17±3
38±5
26±5
23±3
49±6*
> 90% HRpeak (min)
9±2
5±2
14±4
15±4
8±2*
23±5*
Values are in means ± SE. * denotes significantly higher (p<0.05) compared to the
first game.
36 I The physiological impact of soccer on elite... ✍ helena andersson
36
Movement pattern analysis. The game duration was similar (90±0 min) in both
games. The ten players analysed in the movement pattern analysis during games
covered similar total distance (9.4 ± 0.8 km vs 9.9 ± 0.6 km respectively; NS) and
high intensity running distances (1.09 ± 0.47 km vs 1.10 ± 0.43 km respectively; NS)
in both games. The HIR distance ranged between 0.42 -1.98 km in the first game
and 0.61-1.75 km in the second game, showing individual differences in the amount
of work performed during the games. When analysing the HIR distance in 15-min
periods during the games, the distances in the last 30 min of both games were
significantly lower (~24%, p<0.05) compared to the first 15-min period of the
games. The distance covered in HIR in the last 30-min of both games was also ~17%
lower compared to the last 15-min period of the first half (30-45 min) (Fig. 4).
0
50
100
150
200
250
300
0- 15 15- 30 30- 45 45- 60 60- 75 75- 90
Time (min)
Hig
h in
ten
sit
y r
un
nin
g d
ista
nce (m
)
* #
* #
Figure 4. High-intensity running distance in each 15-min period during the games (n=10).
= game 1, = game 2. * denotes significantly lower compared with period 0-15 for both
games. # denotes significantly lower compared with period 30-45 min for both games.
4.1.2 4.1.2 4.1.2 4.1.2 Discussion.Discussion.Discussion.Discussion.
Based on the mean heart-rate values it can be concluded that the aerobic system was
highly taxed during both games. The mean heart rate in both games was similar to
that previously reported in competitive elite female soccer games (Andersson et al.
37
2010; Davis & Brewer 1993; Krustrup et al. 2005). The mean heart rate differed
between the first and second game. Such small inter-match variability (~ 4%) could
be expected between games.
The high mean heart rate, time spent > 85% of HRpeak and HIR distance imply
that the players were able to work at a high intensity in both games. Importantly, the
work intensity (measured as HR) in the second game did not differ between the
active and passive recovery groups. This finding indicates that the active recovery
training did not influence the game performance of players in the second game.
The distance covered in HIR during both games was also similar to what has been
previously reported in high-level competitive female soccer players (Andersson et al.
2010; Gabbett & Mulvey 2008; Krustrup et al. 2005; Mohr et al. 2008), which
confirms that the work performed during the games was high. The reduction of HIR
towards the end of the games may indicate the occurrence of fatigue (Andersson et
al. 2010; Mohr et al. 2008). The facts that the distance in HIR was reduced by the
same extent at the end of both games and that the reduction occurred at a similar
time point (Fig. 4) during the games imply that the players’ performance in the
second game was not affected by the physical stress imposed by the first game.
4.2 NEUROMUSCULAR FATIGUE AND BLOOD MARKERS OF PHYSICAL
STRESS AFTER ELITE FEMALE SOCCER GAMES (PAPER I)
4.2.1 Main findings 4.2.1 Main findings 4.2.1 Main findings 4.2.1 Main findings
The effects of active recovery training. At baseline, there were no significant
differences in absolute values for sprint, CMJ, isokinetic strength, blood CK, urea
and uric acid and perceived muscle soreness between the active and passive recovery
groups. At all time points, we also found no significant differences between the two
groups in the recovery pattern of any of the neuromuscular fatigue and blood
physical stress markers. There was, however, a significant time effect on the
neuromuscular fatigue and blood physical stress markers. As a consequence changes
in these parameters are presented as a mean of both groups.
Neuromuscular fatigue. Sprint performance and knee extensor or flexor strength
decreased immediately after both games with the amplitude of change being
comparable after both games. Sprint performance returned to baseline 5 h after the
first game while peak torque in knee extension and knee flexion returned to baseline
The physiological impact of soccer on elite... ✍ helena andersson I 37
36
Movement pattern analysis. The game duration was similar (90±0 min) in both
games. The ten players analysed in the movement pattern analysis during games
covered similar total distance (9.4 ± 0.8 km vs 9.9 ± 0.6 km respectively; NS) and
high intensity running distances (1.09 ± 0.47 km vs 1.10 ± 0.43 km respectively; NS)
in both games. The HIR distance ranged between 0.42 -1.98 km in the first game
and 0.61-1.75 km in the second game, showing individual differences in the amount
of work performed during the games. When analysing the HIR distance in 15-min
periods during the games, the distances in the last 30 min of both games were
significantly lower (~24%, p<0.05) compared to the first 15-min period of the
games. The distance covered in HIR in the last 30-min of both games was also ~17%
lower compared to the last 15-min period of the first half (30-45 min) (Fig. 4).
0
50
100
150
200
250
300
0- 15 15- 30 30- 45 45- 60 60- 75 75- 90
Time (min)
Hig
h in
ten
sit
y r
un
nin
g d
ista
nce (m
)
* #
* #
Figure 4. High-intensity running distance in each 15-min period during the games (n=10).
= game 1, = game 2. * denotes significantly lower compared with period 0-15 for both
games. # denotes significantly lower compared with period 30-45 min for both games.
4.1.2 4.1.2 4.1.2 4.1.2 Discussion.Discussion.Discussion.Discussion.
Based on the mean heart-rate values it can be concluded that the aerobic system was
highly taxed during both games. The mean heart rate in both games was similar to
that previously reported in competitive elite female soccer games (Andersson et al.
37
2010; Davis & Brewer 1993; Krustrup et al. 2005). The mean heart rate differed
between the first and second game. Such small inter-match variability (~ 4%) could
be expected between games.
The high mean heart rate, time spent > 85% of HRpeak and HIR distance imply
that the players were able to work at a high intensity in both games. Importantly, the
work intensity (measured as HR) in the second game did not differ between the
active and passive recovery groups. This finding indicates that the active recovery
training did not influence the game performance of players in the second game.
The distance covered in HIR during both games was also similar to what has been
previously reported in high-level competitive female soccer players (Andersson et al.
2010; Gabbett & Mulvey 2008; Krustrup et al. 2005; Mohr et al. 2008), which
confirms that the work performed during the games was high. The reduction of HIR
towards the end of the games may indicate the occurrence of fatigue (Andersson et
al. 2010; Mohr et al. 2008). The facts that the distance in HIR was reduced by the
same extent at the end of both games and that the reduction occurred at a similar
time point (Fig. 4) during the games imply that the players’ performance in the
second game was not affected by the physical stress imposed by the first game.
4.2 NEUROMUSCULAR FATIGUE AND BLOOD MARKERS OF PHYSICAL
STRESS AFTER ELITE FEMALE SOCCER GAMES (PAPER I)
4.2.1 Main findings 4.2.1 Main findings 4.2.1 Main findings 4.2.1 Main findings
The effects of active recovery training. At baseline, there were no significant
differences in absolute values for sprint, CMJ, isokinetic strength, blood CK, urea
and uric acid and perceived muscle soreness between the active and passive recovery
groups. At all time points, we also found no significant differences between the two
groups in the recovery pattern of any of the neuromuscular fatigue and blood
physical stress markers. There was, however, a significant time effect on the
neuromuscular fatigue and blood physical stress markers. As a consequence changes
in these parameters are presented as a mean of both groups.
Neuromuscular fatigue. Sprint performance and knee extensor or flexor strength
decreased immediately after both games with the amplitude of change being
comparable after both games. Sprint performance returned to baseline 5 h after the
first game while peak torque in knee extension and knee flexion returned to baseline
38 I The physiological impact of soccer on elite... ✍ helena andersson
38
at 27 h and 51 h after the first game, respectively. CMJ performance decreased
immediately after the first game and remained significantly reduced throughout the
study period. The pre-second game levels for sprint and isokinetic strength, but not
CMJ, had therefore returned to baseline levels before the start of the second game.
As a consequence of the already reduced CMJ levels at the start of the second game,
CMJ did not decline further immediately after the second game.
Blood markers of physical stress. Creatine Kinase, urea and uric acid significantly
increased with similar magnitude after both the first and second games. The peak
value for CK (451±59 U·L-1) was observed 21 h after the game and returned to
baseline levels 69 h after the first game. The peak values for urea and uric acid were
observed immediately after the games and returned to baseline levels 21 h after the
first game. Additionally, changes in perceived muscle soreness followed the same
patterns as CK.
Relationship between blood markers of physical stress and game performance
parameters. The increase in CK levels after the games was significantly related to the
distance covered in HIR during both games (R2= 0.58, r = 0.76, p<0.05) (Fig. 5).
Figure 5 also shows the occurrence of inter-individual differences in the amplitude of
changes in blood physical stress and game performance markers.
100
200
300
400
500
0 500 1000 1500 2000
HIR distance (m)
C
K (
U·L
¹)
R² = 0.58
r = 0.76
Figure 5. Relationship between the distance covered in HIR and acute change in CK
following the first (◊) and second ( games.
39
4.2.3 4.2.3 4.2.3 4.2.3 Discussion Discussion Discussion Discussion
The acute reductions in the performance parameters (sprint, isokinetic knee strength
and CMJ) observed in our study are of similar magnitude to data reported after a
single soccer game or soccer specific running protocol in male players (Ascensão et
al. 2008; Balsom et al. 1993; Krustrup et al. 2006; Oliver et al. 2008). The acute
reductions in CMJ and sprint performance together with the decline in isokinetic
strength indicate that different aspects of the force-generating capacity are
compromised in response to a female soccer game. The reduction in the force-
generating capacity may be caused by structural disruptions within myofibers
(Gibala et al. 1995; Raastad & Hallén 2000), increased inorganic phosphate (Pi),
alterations in the excitation-contraction process (involving alteration in Ca2+ release
and low muscle pH due to lactic acid accumulation) (Warren et al. 2001; Westerblad
et al. 2002), selective glycogen depletion (Krustrup et al. 2006) and impairment of
the stretch-shortening cycle (SSC) (Avela & Komi 1998).
We also observed differences in the recovery time after the game for the different
neuromuscular parameters. Sprint performance was the first physical capacity to
return to baseline after the game (5 h) and was followed by knee extension peak
torque (27 h) and flexion (51 h). CMJ did not recover throughout the remaining
time points of the study. Although strong correlations have been shown between
maximal strength and the performance in sprint and vertical jump (Wisløff et al.
2004) our results suggest differences in the recovery pattern between these physical
qualities. The differences in recovery pattern can be explained by the existence of
differences in the amount of muscle work and in the inter-muscular coordination
between sprint, jump and isokinetic knee flexion and extension (Iossifidou et al.
2005; Jacobs et al. 1996; Jacobs & Schenau 1992).
The long-lasting reductions in jump performance (>72 h) and isokinetic strength
(>45 h) indicate some slow recovering processes within the muscle. Myofibrillar
disruptions have been observed after heavy-strength training and downhill running
(Friden et al. 1981; Gibala et al. 1995). This may have contributed to the long-
lasting reductions in the force-generating capacity though these ideas have not been
directly examined after soccer games.
The increase in blood CK indicates an increased permeability in muscle cell
membranes during the games. The observed increases in uric acid and urea suggest
that soccer games also result in an increase in AMP levels with a subsequent increase
in the formation of ammonia (NH3) as well as the enhancement of protein
The physiological impact of soccer on elite... ✍ helena andersson I 39
38
at 27 h and 51 h after the first game, respectively. CMJ performance decreased
immediately after the first game and remained significantly reduced throughout the
study period. The pre-second game levels for sprint and isokinetic strength, but not
CMJ, had therefore returned to baseline levels before the start of the second game.
As a consequence of the already reduced CMJ levels at the start of the second game,
CMJ did not decline further immediately after the second game.
Blood markers of physical stress. Creatine Kinase, urea and uric acid significantly
increased with similar magnitude after both the first and second games. The peak
value for CK (451±59 U·L-1) was observed 21 h after the game and returned to
baseline levels 69 h after the first game. The peak values for urea and uric acid were
observed immediately after the games and returned to baseline levels 21 h after the
first game. Additionally, changes in perceived muscle soreness followed the same
patterns as CK.
Relationship between blood markers of physical stress and game performance
parameters. The increase in CK levels after the games was significantly related to the
distance covered in HIR during both games (R2= 0.58, r = 0.76, p<0.05) (Fig. 5).
Figure 5 also shows the occurrence of inter-individual differences in the amplitude of
changes in blood physical stress and game performance markers.
100
200
300
400
500
0 500 1000 1500 2000
HIR distance (m)
C
K (
U·L
¹)
R² = 0.58
r = 0.76
Figure 5. Relationship between the distance covered in HIR and acute change in CK
following the first (◊) and second ( games.
39
4.2.3 4.2.3 4.2.3 4.2.3 Discussion Discussion Discussion Discussion
The acute reductions in the performance parameters (sprint, isokinetic knee strength
and CMJ) observed in our study are of similar magnitude to data reported after a
single soccer game or soccer specific running protocol in male players (Ascensão et
al. 2008; Balsom et al. 1993; Krustrup et al. 2006; Oliver et al. 2008). The acute
reductions in CMJ and sprint performance together with the decline in isokinetic
strength indicate that different aspects of the force-generating capacity are
compromised in response to a female soccer game. The reduction in the force-
generating capacity may be caused by structural disruptions within myofibers
(Gibala et al. 1995; Raastad & Hallén 2000), increased inorganic phosphate (Pi),
alterations in the excitation-contraction process (involving alteration in Ca2+ release
and low muscle pH due to lactic acid accumulation) (Warren et al. 2001; Westerblad
et al. 2002), selective glycogen depletion (Krustrup et al. 2006) and impairment of
the stretch-shortening cycle (SSC) (Avela & Komi 1998).
We also observed differences in the recovery time after the game for the different
neuromuscular parameters. Sprint performance was the first physical capacity to
return to baseline after the game (5 h) and was followed by knee extension peak
torque (27 h) and flexion (51 h). CMJ did not recover throughout the remaining
time points of the study. Although strong correlations have been shown between
maximal strength and the performance in sprint and vertical jump (Wisløff et al.
2004) our results suggest differences in the recovery pattern between these physical
qualities. The differences in recovery pattern can be explained by the existence of
differences in the amount of muscle work and in the inter-muscular coordination
between sprint, jump and isokinetic knee flexion and extension (Iossifidou et al.
2005; Jacobs et al. 1996; Jacobs & Schenau 1992).
The long-lasting reductions in jump performance (>72 h) and isokinetic strength
(>45 h) indicate some slow recovering processes within the muscle. Myofibrillar
disruptions have been observed after heavy-strength training and downhill running
(Friden et al. 1981; Gibala et al. 1995). This may have contributed to the long-
lasting reductions in the force-generating capacity though these ideas have not been
directly examined after soccer games.
The increase in blood CK indicates an increased permeability in muscle cell
membranes during the games. The observed increases in uric acid and urea suggest
that soccer games also result in an increase in AMP levels with a subsequent increase
in the formation of ammonia (NH3) as well as the enhancement of protein
40 I The physiological impact of soccer on elite... ✍ helena andersson
40
breakdown. The moderate increase in CK and urea indicates alterations in muscle
membranes and in protein metabolism.
The existence of a relationship between changes in CK and distance in HIR
indicates that the work performed in high speeds during a game is a good indicator
of the stress put on leg muscles during a soccer game (Fig. 5). Moreover, the inter-
individual variability in the amplitude of changes in performance parameters and
physical stress markers after the games may be related to the amount of work
performed by each player in the field and also to the physical fitness status of the
player.
The active recovery training used in this study is widely used by teams in many
countries and is believed to accelerate the recovery after a soccer game. Our results
clearly show that the time course of the recovery of performance parameters and the
blood physical stress markers were not significantly improved by the active recovery
training. Our results are in favour of previous studies in elite athletes suggesting the
lack of evidence supporting the use of active recovery strategies (Barnett 2006; Gill et
al. 2006). Nevertheless, it should be emphasised that low-intensity training did not
have any detrimental effects on recovery.
In conclusion, our data clearly demonstrate the existence of differences in the
recovery pattern of various neuromuscular parameters and physical stress markers in
response to female soccer games. We can conclude that the majority of the
performance parameters (with the exception of CMJ) and physical stress markers
had recovered before the start of the second game. Our data also show that the
recovery time for neuromuscular fatigue and physical stress markers are not
accelerated by active recovery training.
4.3 OXIDATIVE STRESS MARKERS AND ANTIOXIDANT COMPOUNDS AFTER
ELITE FEMALE SOCCER GAMES (PAPER II AND IV).
4.3.1 Main findings 4.3.1 Main findings 4.3.1 Main findings 4.3.1 Main findings
The effects of active recovery training. The active recovery training did not have an
effect on the oxidative stress markers and antioxidant compounds at any time points
during the study. There was, however, a significant time effect in the oxidative stress
markers and antioxidant compounds. For this reason, changes in these parameters
are presented as a mean for both groups.
41
Oxidative stress markers. The analyses of acute changes occurring immediately
after the first and second games revealed a significant increase in GSSG whereas
GSH remained unchanged. As a result of the increased GSSG and unchanged GSH
the GSH:GSSG ratio decreased immediately after both games. The decrease in the
GSH:GSSG ratio was statistically significant only after the first game, however. The
increase in GSSG after the first game was brief as GSSG levels returned to baseline
within 21 h. During the period separating the two games, GSH significantly
decreased at 45 h and 69 h after the first game and thus the pre-second game GSH
levels were lower than the levels prior to the first game. Lipid peroxidation measured
by d-ROMs was not acutely changed after both games and remained unchanged at
all time points except at 69 h when it slightly, but significantly, decreased from
baseline levels.
Endogenous (non-enzymatic) antioxidant compounds. The general response
pattern of the endogenous antioxidants was characterised by a robust increase in
blood immediately after both games. More specifically, both TGSH, UA and FRAP
increased with a similar magnitude after both games. The endogenous antioxidants
cysteine, cysteine-glycine and total thiols also increased after both games. Although
these compounds increased following both games, changes in cysteine, cysteine-
glycine and total thiols were statistically significant only in response to the second
game.
Dietary antioxidant compounds. The response patterns in the dietary antioxidants
showed either a rapid and persistent increase (-tocopherol, total tocopherols and
AA) or a delayed rise (total carotenoids) in blood after the first game (Fig. 6a-d).
Alpha-tocopherol, total tocopherols and AA increased immediately after the first
game and remained elevated at all time points except for a temporary normalisation
of AA at 21 h (Fig. 6c). Consequently, the pre-second game dietary antioxidant levels
of -tocopherol, total tocopherols and AA were higher than the levels prior to the
first game. Immediately after the second game, there were no significant increases in
total tocopherols (Fig. 6a) and AA, whereas -tocopherol slightly decreased. There
were no immediate changes in carotenoids after both the first and the second games
(Fig. 6b). The carotenoids did, however, slowly increase after the first game (starting
at 21 h) and stayed elevated at all further time points. Consequently, the pre-second
game levels of several carotenoids (lutein, -crytpoxanthin, α-carotene, lycopene,
and total carotenoids) were higher than the levels prior to the first game. Finally,
total polyphenols significantly decreased immediately after the first game, remained
The physiological impact of soccer on elite... ✍ helena andersson I 41
40
breakdown. The moderate increase in CK and urea indicates alterations in muscle
membranes and in protein metabolism.
The existence of a relationship between changes in CK and distance in HIR
indicates that the work performed in high speeds during a game is a good indicator
of the stress put on leg muscles during a soccer game (Fig. 5). Moreover, the inter-
individual variability in the amplitude of changes in performance parameters and
physical stress markers after the games may be related to the amount of work
performed by each player in the field and also to the physical fitness status of the
player.
The active recovery training used in this study is widely used by teams in many
countries and is believed to accelerate the recovery after a soccer game. Our results
clearly show that the time course of the recovery of performance parameters and the
blood physical stress markers were not significantly improved by the active recovery
training. Our results are in favour of previous studies in elite athletes suggesting the
lack of evidence supporting the use of active recovery strategies (Barnett 2006; Gill et
al. 2006). Nevertheless, it should be emphasised that low-intensity training did not
have any detrimental effects on recovery.
In conclusion, our data clearly demonstrate the existence of differences in the
recovery pattern of various neuromuscular parameters and physical stress markers in
response to female soccer games. We can conclude that the majority of the
performance parameters (with the exception of CMJ) and physical stress markers
had recovered before the start of the second game. Our data also show that the
recovery time for neuromuscular fatigue and physical stress markers are not
accelerated by active recovery training.
4.3 OXIDATIVE STRESS MARKERS AND ANTIOXIDANT COMPOUNDS AFTER
ELITE FEMALE SOCCER GAMES (PAPER II AND IV).
4.3.1 Main findings 4.3.1 Main findings 4.3.1 Main findings 4.3.1 Main findings
The effects of active recovery training. The active recovery training did not have an
effect on the oxidative stress markers and antioxidant compounds at any time points
during the study. There was, however, a significant time effect in the oxidative stress
markers and antioxidant compounds. For this reason, changes in these parameters
are presented as a mean for both groups.
41
Oxidative stress markers. The analyses of acute changes occurring immediately
after the first and second games revealed a significant increase in GSSG whereas
GSH remained unchanged. As a result of the increased GSSG and unchanged GSH
the GSH:GSSG ratio decreased immediately after both games. The decrease in the
GSH:GSSG ratio was statistically significant only after the first game, however. The
increase in GSSG after the first game was brief as GSSG levels returned to baseline
within 21 h. During the period separating the two games, GSH significantly
decreased at 45 h and 69 h after the first game and thus the pre-second game GSH
levels were lower than the levels prior to the first game. Lipid peroxidation measured
by d-ROMs was not acutely changed after both games and remained unchanged at
all time points except at 69 h when it slightly, but significantly, decreased from
baseline levels.
Endogenous (non-enzymatic) antioxidant compounds. The general response
pattern of the endogenous antioxidants was characterised by a robust increase in
blood immediately after both games. More specifically, both TGSH, UA and FRAP
increased with a similar magnitude after both games. The endogenous antioxidants
cysteine, cysteine-glycine and total thiols also increased after both games. Although
these compounds increased following both games, changes in cysteine, cysteine-
glycine and total thiols were statistically significant only in response to the second
game.
Dietary antioxidant compounds. The response patterns in the dietary antioxidants
showed either a rapid and persistent increase (-tocopherol, total tocopherols and
AA) or a delayed rise (total carotenoids) in blood after the first game (Fig. 6a-d).
Alpha-tocopherol, total tocopherols and AA increased immediately after the first
game and remained elevated at all time points except for a temporary normalisation
of AA at 21 h (Fig. 6c). Consequently, the pre-second game dietary antioxidant levels
of -tocopherol, total tocopherols and AA were higher than the levels prior to the
first game. Immediately after the second game, there were no significant increases in
total tocopherols (Fig. 6a) and AA, whereas -tocopherol slightly decreased. There
were no immediate changes in carotenoids after both the first and the second games
(Fig. 6b). The carotenoids did, however, slowly increase after the first game (starting
at 21 h) and stayed elevated at all further time points. Consequently, the pre-second
game levels of several carotenoids (lutein, -crytpoxanthin, α-carotene, lycopene,
and total carotenoids) were higher than the levels prior to the first game. Finally,
total polyphenols significantly decreased immediately after the first game, remained
42 I The physiological impact of soccer on elite... ✍ helena andersson
42
reduced until 69 h after the first game and were then unchanged after the second
game (Fig. 6d). Finally, as shown in figure 6 a-d, the amplitude of changes in
oxidative stress markers and antioxidant compounds after the games varied between
players.
Figure 6 a-d. Changes in dietary antioxidant compounds in female elite soccer players
during two games separated by 72-h recovery. Values are relative changes (%) from
baseline and each curve represents an individual player: a) total tocopherols b) total
carotenoids c) AA and d) total polyphenols. IP = immediately post games. * denotes
significant changes compared to baseline (P<0.05).
4.3.2 4.3.2 4.3.2 4.3.2 DiscDiscDiscDiscussion ussion ussion ussion
The significant increase in blood GSSG observed immediately after the games
indicates increased ROS production. Considering that 2-5% of total 2
•
VO results in
6
43
the formation of ROS (Jackson 1998), and that the players worked at an intensity
level of ~85% of HRpeak (approximately 67% of 2
•
VO peak) (Table 1), an increased
production of ROS during the soccer game was expected. The increase in GSSG led
to a decreased GSH:GSSG ratio after both games (statistically significant only after
the first game). Prior to the second game the GSH:GSSG ratio was already reduced
compared to baseline. This may explain why the decrease in GSH:GSSG ratio was
statistically significant only after the first game and not after the second game.
Interestingly, our study showed no significant changes in the level of d-ROMs after
both games. Previous studies in male players showed increased lipid peroxidation
(measured by malondialdehyde, MDA and thioburbiuric acid-reactive substances,
TBARS) in plasma following a single soccer game (Ascensão et al. 2008; Ispirlidis et
al. 2008). The opposite results between our study performed on elite female players
and those from Ascensão et al. (2008) and Ispirlidis et al. (2008) performed on non
elite male players may be explained by an improved protection against oxidative
insults in well-trained athletes (Brites et al. 1999; Cazzola et al. 2003) or by the
protective effects of oestrogens (Kendall & Eston 2002). It has been shown that
trained women have lower resting MDA levels that those of to trained men (Bloomer
& Fisher-Wellman 2008). This indicates that sex differences in the response of
oxidative stress markers and antioxidant levels may exist in soccer players.
Increases in ROS may modulate a variety of cellular processes that may cause
structural changes in the muscle fibres and reduction of muscle contractile function
(Peake et al. 2007). For example, increased ROS can affect sarcolemmal function
(Dudley et al. 2006), calcium regulation (Abramson & Salama 1989), myofilament
interaction (Callahan et al. 2001), and mitochondrial metabolism (Hauser et al.
1995; Pruijn & Schoonen 1992). It is therefore possible that the increased GSSG
observed after the games may have contributed to the decline in force-generating
capacities (reduced performance parameters). However, no significant correlations
were observed between the neuromuscular fatigue parameters and GSSG levels after
the games.
Our study showed for the first time the occurrence of a strong soccer-game-
induced endogenous antioxidant response in female players. TGSH, UA and FRAP
increased with similar amplitude after both games. Although the endogenous
antioxidants cysteine, cysteine-glycine and total thiols also increased after both
games, changes in the level of these antioxidants reached a statistically significant
level only after the second game. Our data therefore indicate that endogenous
The physiological impact of soccer on elite... ✍ helena andersson I 43
42
reduced until 69 h after the first game and were then unchanged after the second
game (Fig. 6d). Finally, as shown in figure 6 a-d, the amplitude of changes in
oxidative stress markers and antioxidant compounds after the games varied between
players.
Figure 6 a-d. Changes in dietary antioxidant compounds in female elite soccer players
during two games separated by 72-h recovery. Values are relative changes (%) from
baseline and each curve represents an individual player: a) total tocopherols b) total
carotenoids c) AA and d) total polyphenols. IP = immediately post games. * denotes
significant changes compared to baseline (P<0.05).
4.3.2 4.3.2 4.3.2 4.3.2 DiscDiscDiscDiscussion ussion ussion ussion
The significant increase in blood GSSG observed immediately after the games
indicates increased ROS production. Considering that 2-5% of total 2
•
VO results in
6
43
the formation of ROS (Jackson 1998), and that the players worked at an intensity
level of ~85% of HRpeak (approximately 67% of 2
•
VO peak) (Table 1), an increased
production of ROS during the soccer game was expected. The increase in GSSG led
to a decreased GSH:GSSG ratio after both games (statistically significant only after
the first game). Prior to the second game the GSH:GSSG ratio was already reduced
compared to baseline. This may explain why the decrease in GSH:GSSG ratio was
statistically significant only after the first game and not after the second game.
Interestingly, our study showed no significant changes in the level of d-ROMs after
both games. Previous studies in male players showed increased lipid peroxidation
(measured by malondialdehyde, MDA and thioburbiuric acid-reactive substances,
TBARS) in plasma following a single soccer game (Ascensão et al. 2008; Ispirlidis et
al. 2008). The opposite results between our study performed on elite female players
and those from Ascensão et al. (2008) and Ispirlidis et al. (2008) performed on non
elite male players may be explained by an improved protection against oxidative
insults in well-trained athletes (Brites et al. 1999; Cazzola et al. 2003) or by the
protective effects of oestrogens (Kendall & Eston 2002). It has been shown that
trained women have lower resting MDA levels that those of to trained men (Bloomer
& Fisher-Wellman 2008). This indicates that sex differences in the response of
oxidative stress markers and antioxidant levels may exist in soccer players.
Increases in ROS may modulate a variety of cellular processes that may cause
structural changes in the muscle fibres and reduction of muscle contractile function
(Peake et al. 2007). For example, increased ROS can affect sarcolemmal function
(Dudley et al. 2006), calcium regulation (Abramson & Salama 1989), myofilament
interaction (Callahan et al. 2001), and mitochondrial metabolism (Hauser et al.
1995; Pruijn & Schoonen 1992). It is therefore possible that the increased GSSG
observed after the games may have contributed to the decline in force-generating
capacities (reduced performance parameters). However, no significant correlations
were observed between the neuromuscular fatigue parameters and GSSG levels after
the games.
Our study showed for the first time the occurrence of a strong soccer-game-
induced endogenous antioxidant response in female players. TGSH, UA and FRAP
increased with similar amplitude after both games. Although the endogenous
antioxidants cysteine, cysteine-glycine and total thiols also increased after both
games, changes in the level of these antioxidants reached a statistically significant
level only after the second game. Our data therefore indicate that endogenous
44 I The physiological impact of soccer on elite... ✍ helena andersson
44
antioxidants may play an important role in the antioxidant defence during the acute
phase following intermittent exercise. Generally, the workload induced by a soccer
game is able to stimulate a strong acute endogenous antioxidant response which
seems to be maintained during repeated soccer games.
The acute increase in blood levels of the dietary antioxidants tocopherols and AA
and decrease of polyphenols after the first game indicate a role of some dietary
antioxidants in the early line of defence against increased ROS production. Contrary
to the rapid normalisation of the endogenous antioxidants, however, there was a
persistent elevation of AA and tocopherols and reduction of polyphenols after the
first game. The long-lasting changes of these dietary antioxidant compounds suggest
that they are involved in the stabilisation and maintenance of homeostasis in the
redox-balance several days following the first soccer game. As the response of these
dietary antioxidants was long-lasting, they did not further increase immediately after
the second game, thereby suggesting sufficient levels of available dietary antioxidants
in the circulation during the second soccer game.
There were no acute changes in the carotenoids following the games suggesting
that carotenoids are not involved in the acute response to increased ROS after
exercise. We did, however, observe a delayed and persistent increase of carotenoids
starting 21 h after the first game. This recruitment pattern suggests that carotenoids
are slowly mobilised from their storage sites (such as the adipose tissue) possibly to
strengthen the blood antioxidant capacity in response to the soccer game.
The active recovery training had no influence on the restoration of oxidative stress
markers and antioxidant levels during repeated soccer games in elite female players.
Furthermore, increases in GSSG are associated with exercise intensity (Ji et al. 1992)
and the low-intensity recovery training in the time period after the first game did not
cause increased GSSG.
Similarly to the game-performance parameters (e.g., HR and HIR), inter-
individual differences were observed in the amplitude of changes in oxidative stress
markers and antioxidant levels after the games. The increase in free-radical
production and antioxidants is related to the increase in oxygen consumption that
occurs during exercise. Therefore, the inter-individual variability in oxidative stress
markers and antioxidants can be related to the amount of aerobic work performed
by the players during the games. However, we failed to show a relationship between
the workload (measured as HR) during the games and increases in GSSG or
antioxidants after the games.
45
Figure 7. Interaction between oxidative stress markers and endogenous and dietary
antioxidants following a soccer game in well-trained female soccer players.
In conclusion, our results suggest a model in which the concomitant increase in
endogenous and dietary antioxidants in response to the transient increase in GSSG
prevented the occurrence of lipid peroxidation measured by d-ROMs in well-trained
female players (Fig. 7). The robust but brief increases in the endogenous antioxidants
after the games indicate their involvement in the acute response to increased free-
radical production. The dietary antioxidant response seems to be related to both the
acute defence against increased free-radical production and to the maintenance of a
prolonged balanced redox after a female soccer game. Finally, the use of active
recovery training in the period between two elite female soccer games had no impact
on the oxidative stress and antioxidant systems.
GSSG GSH:GSSG
SOCCER GAME FOR ELITE FEMALE PLAYERS
Unchanged d-ROMs
ANTI-OXIDANTS PRO-OXIDANTS
POLYPHENOLS
ENDOGENOUS & DIETARY ANTIOXIDANTS
?
The physiological impact of soccer on elite... ✍ helena andersson I 45
44
antioxidants may play an important role in the antioxidant defence during the acute
phase following intermittent exercise. Generally, the workload induced by a soccer
game is able to stimulate a strong acute endogenous antioxidant response which
seems to be maintained during repeated soccer games.
The acute increase in blood levels of the dietary antioxidants tocopherols and AA
and decrease of polyphenols after the first game indicate a role of some dietary
antioxidants in the early line of defence against increased ROS production. Contrary
to the rapid normalisation of the endogenous antioxidants, however, there was a
persistent elevation of AA and tocopherols and reduction of polyphenols after the
first game. The long-lasting changes of these dietary antioxidant compounds suggest
that they are involved in the stabilisation and maintenance of homeostasis in the
redox-balance several days following the first soccer game. As the response of these
dietary antioxidants was long-lasting, they did not further increase immediately after
the second game, thereby suggesting sufficient levels of available dietary antioxidants
in the circulation during the second soccer game.
There were no acute changes in the carotenoids following the games suggesting
that carotenoids are not involved in the acute response to increased ROS after
exercise. We did, however, observe a delayed and persistent increase of carotenoids
starting 21 h after the first game. This recruitment pattern suggests that carotenoids
are slowly mobilised from their storage sites (such as the adipose tissue) possibly to
strengthen the blood antioxidant capacity in response to the soccer game.
The active recovery training had no influence on the restoration of oxidative stress
markers and antioxidant levels during repeated soccer games in elite female players.
Furthermore, increases in GSSG are associated with exercise intensity (Ji et al. 1992)
and the low-intensity recovery training in the time period after the first game did not
cause increased GSSG.
Similarly to the game-performance parameters (e.g., HR and HIR), inter-
individual differences were observed in the amplitude of changes in oxidative stress
markers and antioxidant levels after the games. The increase in free-radical
production and antioxidants is related to the increase in oxygen consumption that
occurs during exercise. Therefore, the inter-individual variability in oxidative stress
markers and antioxidants can be related to the amount of aerobic work performed
by the players during the games. However, we failed to show a relationship between
the workload (measured as HR) during the games and increases in GSSG or
antioxidants after the games.
45
Figure 7. Interaction between oxidative stress markers and endogenous and dietary
antioxidants following a soccer game in well-trained female soccer players.
In conclusion, our results suggest a model in which the concomitant increase in
endogenous and dietary antioxidants in response to the transient increase in GSSG
prevented the occurrence of lipid peroxidation measured by d-ROMs in well-trained
female players (Fig. 7). The robust but brief increases in the endogenous antioxidants
after the games indicate their involvement in the acute response to increased free-
radical production. The dietary antioxidant response seems to be related to both the
acute defence against increased free-radical production and to the maintenance of a
prolonged balanced redox after a female soccer game. Finally, the use of active
recovery training in the period between two elite female soccer games had no impact
on the oxidative stress and antioxidant systems.
GSSG GSH:GSSG
SOCCER GAME FOR ELITE FEMALE PLAYERS
Unchanged d-ROMs
ANTI-OXIDANTS PRO-OXIDANTS
POLYPHENOLS
ENDOGENOUS & DIETARY ANTIOXIDANTS
?
46 I The physiological impact of soccer on elite... ✍ helena andersson
46
4.4 INFLAMMATORY RESPONSE AFTER ELITE FEMALE SOCCER GAMES
(PAPER III)
4.4.14.4.14.4.14.4.1 Main findings Main findings Main findings Main findings
The effects of active recovery training. There were no differences in the cytokine
response between the passive and the active recovery groups at any of the time
points. Importantly, there was a significant time effect on the inflammatory cytokine
response. For this reason, changes in plasma cytokines and leukocyte cell count at
different time points in the experiments are presented as a mean for both groups.
Leukocyte cell count. Total leukocyte and neutrophil cell counts increased
similarly following both games and returned to baseline levels within 21 h after the
first game.
Cytokine response. Immediately after the first game significant elevations in
plasma concentration of twelve cytokines (IL-12, TNF-α, INF-, IL-6, IL-2R, IL-4,
IL-5, IL-7, IL-10, IL-13, IL-17, and INF-α) and three chemokines (IL-8, MIG, and
MCP-1) were observed (Fig. 8a-d). All cytokines and chemokines returned to
baseline levels within 21 h after the first game and remained at baseline levels until
the beginning of the second game. The cytokine response following the second game
differed from that of the first game. Only two cytokines, IL-12 and IL-6, and the
same chemokines IL-8, MIG and MCP-1 increased significantly after the second
game. The amplitude of changes of these cytokines and chemokines after the second
game was of similar amplitude to that seen after the first game (Fig. 8b-d).
47
Figure 8. Plasma inflammatory cytokine response in female elite soccer players during two
games separated by 72-h recovery. Values are absolute changes (mean ± SE) from baseline:
a) anti-inflammatory cytokines, b) IL-6, c) pro-inflammatory cytokines and d) chemokines:
IP = immediately post games: * denotes significantly higher than baseline (P<0.05).
4.4.24.4.24.4.24.4.2 Discussion Discussion Discussion Discussion
It has been shown that neutrophil cell counts increase progressively with exercise
intensity (Sureda et al. 2009). Here we show that neutrophil cell counts increased
similarly following both games. This is in accordance with the fact that both games
in the present study were of a comparable intensity. The amplitude of the increase of
cell counts and the time to return to baseline levels are in agreement with data
reported in male players (Ascensão et al. 2008; Ispirlidis et al. 2008). This would
suggest the absence of sex differences in the leukocyte response after soccer games. It
The physiological impact of soccer on elite... ✍ helena andersson I 47
46
4.4 INFLAMMATORY RESPONSE AFTER ELITE FEMALE SOCCER GAMES
(PAPER III)
4.4.14.4.14.4.14.4.1 Main findings Main findings Main findings Main findings
The effects of active recovery training. There were no differences in the cytokine
response between the passive and the active recovery groups at any of the time
points. Importantly, there was a significant time effect on the inflammatory cytokine
response. For this reason, changes in plasma cytokines and leukocyte cell count at
different time points in the experiments are presented as a mean for both groups.
Leukocyte cell count. Total leukocyte and neutrophil cell counts increased
similarly following both games and returned to baseline levels within 21 h after the
first game.
Cytokine response. Immediately after the first game significant elevations in
plasma concentration of twelve cytokines (IL-12, TNF-α, INF-, IL-6, IL-2R, IL-4,
IL-5, IL-7, IL-10, IL-13, IL-17, and INF-α) and three chemokines (IL-8, MIG, and
MCP-1) were observed (Fig. 8a-d). All cytokines and chemokines returned to
baseline levels within 21 h after the first game and remained at baseline levels until
the beginning of the second game. The cytokine response following the second game
differed from that of the first game. Only two cytokines, IL-12 and IL-6, and the
same chemokines IL-8, MIG and MCP-1 increased significantly after the second
game. The amplitude of changes of these cytokines and chemokines after the second
game was of similar amplitude to that seen after the first game (Fig. 8b-d).
47
Figure 8. Plasma inflammatory cytokine response in female elite soccer players during two
games separated by 72-h recovery. Values are absolute changes (mean ± SE) from baseline:
a) anti-inflammatory cytokines, b) IL-6, c) pro-inflammatory cytokines and d) chemokines:
IP = immediately post games: * denotes significantly higher than baseline (P<0.05).
4.4.24.4.24.4.24.4.2 Discussion Discussion Discussion Discussion
It has been shown that neutrophil cell counts increase progressively with exercise
intensity (Sureda et al. 2009). Here we show that neutrophil cell counts increased
similarly following both games. This is in accordance with the fact that both games
in the present study were of a comparable intensity. The amplitude of the increase of
cell counts and the time to return to baseline levels are in agreement with data
reported in male players (Ascensão et al. 2008; Ispirlidis et al. 2008). This would
suggest the absence of sex differences in the leukocyte response after soccer games. It
48 I The physiological impact of soccer on elite... ✍ helena andersson
48
can also be concluded that leukocyte mobilisation is similar during repeated soccer
games that are separated by 72 h.
Our study clearly showed a robust, but transient, increase in several pro- and anti-
inflammatory cytokines and chemokines after the first game. It can be hypothesized
that the cytokine release following the games might have been triggered by increases
in catecholamines and cortisol, changes in metabolic activity, the occurrence of
membrane disruptions in muscle cells, and increased free-radical production
(Nieman et al. 2005; Steensberg et al. 2003; Suzuki et al. 2000). The large cytokine
response after the first soccer game may also be explained by interactions between
cytokines. All pro-and anti-inflammatory cytokines and chemokines had returned to
baseline within 21 h and thus were within normal baseline ranges at the start of the
second game.
Another main finding was the unexpectedly dampened cytokine response after the
second game. There are several possible hypotheses behind this phenomenon. First, it
has been shown that the cytokine response during exercise is dependent on the
exercise intensity and duration (Pedersen 2000). Our results indicate that the
intensity in both games was comparable or even slightly higher in the second game.
The dampened cytokine response can therefore not be explained by a lower game
intensity in the second game. It has also been reported that carbohydrate (CHO)
loading attenuates the cytokine response following exercise (Bishop et al. 2002;
Chan et al. 2003) and that CHO availability may influence the magnitude of the
post-exercise disturbance in markers of immune function (Cox et al. 2008). In the
present study, diet was carefully supervised several days before the second game but
for only two meals before the first game. Thus, there is a possibility that the muscle
CHO levels before the second game were higher than those before the first game. A
third possible explanation is that a second bout of exercise would cause a dampening
of the inflammatory response (Pizza et al. 2001). This concept is called the “repeated
bout effect” (McHugh 2003). This phenomenon is, however, reported to occur
mostly in untrained subjects (Nikolaidis et al. 2007; Pizza et al. 2001). As the players
in our study were well-trained, it seems unlikely that the dampened cytokine
response was due to the repeated bout effect. The dampened cytokine response may
also be the result of a fast suppressive counter-regulation (Weinstock et al. 1997).
The second game was played 72 h after the first game and whether a fast systemic
counter-regulation following the first game might occur and influence the cytokine
response in a second game played 72 h later is unknown. Finally, it has been
49
suggested that high levels of antioxidants (using antioxidant supplements) attenuates
cytokine production (Fischer et al. 2004; Vassilakopoulos et al. 2003). In our study,
several dietary antioxidants were significantly elevated both prior to and directly
after the second game. The dampened cytokine response may therefore be connected
to the high blood antioxidant levels observed before and after the second game.
The active recovery training performed 22 and 46 h after the first game did not
affect the inflammatory mediators in elite female players. This finding is similar to
data reported in previous studies where strategies as active recovery or cold-water
immersion did not accelerate the recovery of several neuromuscular or physical stress
markers (Gill et al. 2006; Kinugasa & Kilding 2009; Tessitore; 2008) and cytokine
response (Rowsell et al. 2009) following intermittent exercise.
It is suggested that the structural changes occurring in the muscle fibre during
exercise elicit a repair response when the mechanical disruption of myofibers initiates
local and systemic production of cytokines (Pedersen & Hoffman-Goetz 2000).
Consequently, increased cytokine levels have mainly been associated to eccentric
muscle actions and it has been suggested that muscle damage (indicated by elevated
CK) is associated with increases in cytokines, such as IL-6 (Bruunsgaard et al. 1997;
Nieman et al. 2005). However, other studies have failed to find a correlation
between IL-6 and muscle damage (Croisier et al. 1999; Ostrowski et al. 1998a;
Ostrowski et al. 2000). It has therefore been suggested that exercise-induced muscle
damage is not the major cause of increased plasma IL-6 concentrations following
eccentric exercise (Peake et al. 2005c). In the present study we did not find any
correlation between changes in CK and IL-6 or any of the other cytokines. Our
results do not support the existence of a relationship between muscle damage
markers and changes in cytokines.
The production of cytokines following exercise has also been closely associated
with increases in neutrophil cell counts (Suzuki et al. 1999). We did not however
find a relationship between the amplitude of plasma cytokine changes and the
amplitude of neutrophil cell count changes.
In conclusion, this study shows that one single elite female soccer game leads to an
immediate mobilisation of immune cells and a robust, but transient, increase in
plasma concentration of both pro- and anti-inflammatory cytokines. Our data show
that when a second game is played 72 h after the first game a dampened cytokine
response occurs. The mechanisms and the practical implications of the dampened
cytokine response are unknown. Our findings indicate that active recovery training
The physiological impact of soccer on elite... ✍ helena andersson I 49
48
can also be concluded that leukocyte mobilisation is similar during repeated soccer
games that are separated by 72 h.
Our study clearly showed a robust, but transient, increase in several pro- and anti-
inflammatory cytokines and chemokines after the first game. It can be hypothesized
that the cytokine release following the games might have been triggered by increases
in catecholamines and cortisol, changes in metabolic activity, the occurrence of
membrane disruptions in muscle cells, and increased free-radical production
(Nieman et al. 2005; Steensberg et al. 2003; Suzuki et al. 2000). The large cytokine
response after the first soccer game may also be explained by interactions between
cytokines. All pro-and anti-inflammatory cytokines and chemokines had returned to
baseline within 21 h and thus were within normal baseline ranges at the start of the
second game.
Another main finding was the unexpectedly dampened cytokine response after the
second game. There are several possible hypotheses behind this phenomenon. First, it
has been shown that the cytokine response during exercise is dependent on the
exercise intensity and duration (Pedersen 2000). Our results indicate that the
intensity in both games was comparable or even slightly higher in the second game.
The dampened cytokine response can therefore not be explained by a lower game
intensity in the second game. It has also been reported that carbohydrate (CHO)
loading attenuates the cytokine response following exercise (Bishop et al. 2002;
Chan et al. 2003) and that CHO availability may influence the magnitude of the
post-exercise disturbance in markers of immune function (Cox et al. 2008). In the
present study, diet was carefully supervised several days before the second game but
for only two meals before the first game. Thus, there is a possibility that the muscle
CHO levels before the second game were higher than those before the first game. A
third possible explanation is that a second bout of exercise would cause a dampening
of the inflammatory response (Pizza et al. 2001). This concept is called the “repeated
bout effect” (McHugh 2003). This phenomenon is, however, reported to occur
mostly in untrained subjects (Nikolaidis et al. 2007; Pizza et al. 2001). As the players
in our study were well-trained, it seems unlikely that the dampened cytokine
response was due to the repeated bout effect. The dampened cytokine response may
also be the result of a fast suppressive counter-regulation (Weinstock et al. 1997).
The second game was played 72 h after the first game and whether a fast systemic
counter-regulation following the first game might occur and influence the cytokine
response in a second game played 72 h later is unknown. Finally, it has been
49
suggested that high levels of antioxidants (using antioxidant supplements) attenuates
cytokine production (Fischer et al. 2004; Vassilakopoulos et al. 2003). In our study,
several dietary antioxidants were significantly elevated both prior to and directly
after the second game. The dampened cytokine response may therefore be connected
to the high blood antioxidant levels observed before and after the second game.
The active recovery training performed 22 and 46 h after the first game did not
affect the inflammatory mediators in elite female players. This finding is similar to
data reported in previous studies where strategies as active recovery or cold-water
immersion did not accelerate the recovery of several neuromuscular or physical stress
markers (Gill et al. 2006; Kinugasa & Kilding 2009; Tessitore; 2008) and cytokine
response (Rowsell et al. 2009) following intermittent exercise.
It is suggested that the structural changes occurring in the muscle fibre during
exercise elicit a repair response when the mechanical disruption of myofibers initiates
local and systemic production of cytokines (Pedersen & Hoffman-Goetz 2000).
Consequently, increased cytokine levels have mainly been associated to eccentric
muscle actions and it has been suggested that muscle damage (indicated by elevated
CK) is associated with increases in cytokines, such as IL-6 (Bruunsgaard et al. 1997;
Nieman et al. 2005). However, other studies have failed to find a correlation
between IL-6 and muscle damage (Croisier et al. 1999; Ostrowski et al. 1998a;
Ostrowski et al. 2000). It has therefore been suggested that exercise-induced muscle
damage is not the major cause of increased plasma IL-6 concentrations following
eccentric exercise (Peake et al. 2005c). In the present study we did not find any
correlation between changes in CK and IL-6 or any of the other cytokines. Our
results do not support the existence of a relationship between muscle damage
markers and changes in cytokines.
The production of cytokines following exercise has also been closely associated
with increases in neutrophil cell counts (Suzuki et al. 1999). We did not however
find a relationship between the amplitude of plasma cytokine changes and the
amplitude of neutrophil cell count changes.
In conclusion, this study shows that one single elite female soccer game leads to an
immediate mobilisation of immune cells and a robust, but transient, increase in
plasma concentration of both pro- and anti-inflammatory cytokines. Our data show
that when a second game is played 72 h after the first game a dampened cytokine
response occurs. The mechanisms and the practical implications of the dampened
cytokine response are unknown. Our findings indicate that active recovery training
50 I The physiological impact of soccer on elite... ✍ helena andersson
50
does not influence the recovery pattern of inflammatory parameters in elite female
soccer players. This is in accordance with the lack of effects of this recovery strategy
on neuromuscular and physical stress parameters, oxidative stress markers and
antioxidant levels.
51
5 CONCLUSIONS
Female soccer is one of the fastest growing sports in the world. There are, however,
limited scientific data on how elite female players respond to the physical stress
imposed by a soccer game. Additionally, knowledge about the recovery processes
following a game is also limited. Efficient recovery following a game in international
tournaments is important since there are few recovery days between games. The
present thesis was designed to mirror an actual competitive situation for elite female
players in order to study the physiological impact of soccer on female players and to
better understand the recovery of several physiological systems during two repeated
soccer games.
5.1 MAIN FINDINGS OF THE THESIS
i ) Immediately after one soccer game in elite female players a reduction in
performance parameters was observed indicating the occurrence of
neuromuscular fatigue. Increases in blood markers of physical stress and
perceived muscle soreness also occurred immediately after a game. The first game
resulted in the enhancement of free-radical production and the concomitant
recruitment of endogenous and some dietary antioxidant compounds, which
maintained the redox balance. A balanced recruitment of several pro-and anti-
inflammatory cytokines also occurred.
ii) During the 72-h recovery following the first game, marked differences occurred
in the recovery pattern of the various performance and blood physical stress
markers. In general, the majority of the neuromuscular fatigue parameters (with
the exception of CMJ) and physical stress markers had returned to baseline levels
before the start of the second game. The changes that occurred in blood oxidative
stress markers and endogenous antioxidants after the first game were brief and
had returned to baseline levels within 21 h. The changes in blood levels of dietary
antioxidants were, however, more long-lasting. The soccer-game-induced
increases in the inflammatory cytokines were brief and had returned to baseline
levels within 21 h after the first game.
The physiological impact of soccer on elite... ✍ helena andersson I 51
50
does not influence the recovery pattern of inflammatory parameters in elite female
soccer players. This is in accordance with the lack of effects of this recovery strategy
on neuromuscular and physical stress parameters, oxidative stress markers and
antioxidant levels.
51
5 CONCLUSIONS
Female soccer is one of the fastest growing sports in the world. There are, however,
limited scientific data on how elite female players respond to the physical stress
imposed by a soccer game. Additionally, knowledge about the recovery processes
following a game is also limited. Efficient recovery following a game in international
tournaments is important since there are few recovery days between games. The
present thesis was designed to mirror an actual competitive situation for elite female
players in order to study the physiological impact of soccer on female players and to
better understand the recovery of several physiological systems during two repeated
soccer games.
5.1 MAIN FINDINGS OF THE THESIS
i ) Immediately after one soccer game in elite female players a reduction in
performance parameters was observed indicating the occurrence of
neuromuscular fatigue. Increases in blood markers of physical stress and
perceived muscle soreness also occurred immediately after a game. The first game
resulted in the enhancement of free-radical production and the concomitant
recruitment of endogenous and some dietary antioxidant compounds, which
maintained the redox balance. A balanced recruitment of several pro-and anti-
inflammatory cytokines also occurred.
ii) During the 72-h recovery following the first game, marked differences occurred
in the recovery pattern of the various performance and blood physical stress
markers. In general, the majority of the neuromuscular fatigue parameters (with
the exception of CMJ) and physical stress markers had returned to baseline levels
before the start of the second game. The changes that occurred in blood oxidative
stress markers and endogenous antioxidants after the first game were brief and
had returned to baseline levels within 21 h. The changes in blood levels of dietary
antioxidants were, however, more long-lasting. The soccer-game-induced
increases in the inflammatory cytokines were brief and had returned to baseline
levels within 21 h after the first game.
52 I The physiological impact of soccer on elite... ✍ helena andersson
52
iii) The low-intensity recovery training performed between two games did not
influence the recovery time of the performance parameters, blood physical stress
markers, the restoration of the redox balance or the inflammatory parameters in
elite female players.
iv) Two repeated elite female soccer games induced similar acute changes in the
neuromuscular fatigue parameters (with the exception of CMJ), elevation in
blood physical stress markers and perceived muscle soreness. Similar acute
oxidative stress reactions and recruitment of endogenous antioxidants occurred
after both games. The dietary antioxidants (with the exception of carotenoids),
however, had dissimilar acute recruitment patterns after both games. Dissimilar
inflammatory responses also occurred after the two games, with a marked
damped cytokine response after the second game.
5.2 IMPLICATIONS
In general, the recovery patterns of the soccer-induced changes in neuromuscular
fatigue parameters, physical stress markers, the redox status and inflammatory
parameters indicate that 72 h between two games is an adequate recovery period in
elite female soccer players. An inter-individual variability in the amplitude of soccer-
induced changes in the physiological variables occured and may be related to the
amount of work performed by each player in the field. It is important to highlight
the fact that the game performance (HIR distance and HR) in the second game was
also not affected by the physiological changes imposed by the first game. However,
the fact that CMJ did not recover during the 72-h period after the first game
indicates that a particular attention should be devoted to the training of explosive
force.
Since the amount of HIR distance during the game was correlated to changes in
CK, HIR may be a useful indicator of the stress put on leg muscles during a game
and may help to individualise the recovery period in soccer players.
Low-intensive recovery training performed at 22 and 45 h after the first game did
not accelerate the recovery of neuromuscular fatigue and physical stress markers, the
redox-balance or the inflammatory response in elite female players. The potential
benefits behind the use of this post-game recovery strategy are not supported by our
53
data. Nevertheless, because of the lack of both positive and negative effects on
recovery, it is suggested that low-intensity exercise can be performed in the recovery
period between soccer games without risks of deteriorating performance in
upcoming games.
This thesis demonstrated the effectiveness of the antioxidant systems in elite
female soccer players. Based on our findings, the regular use of antioxidant
supplements in well-trained female athletes may be questionable. It has been shown
that supplementation with vitamin C may inhibit cellular adaptations to exercise
because it prevents the expression of key transcription factors involved in
mitochondrial biogenesis (Gomez-Cabrera et al. 2008a). The use of supplementation
in elite female players may interfere with soccer-induced training adaptations and
should not be recommended.
The strong pro- and anti-inflammatory cytokine response observed after one single
soccer game in the female players might be an important factor involved in the
adaptation to regular training. The use of anti-inflammatory drugs may therefore
interfere with training adaptations. In this respect, it has been suggested that the use
of nonsteroidal anti-inflammatory drugs (NSAIDs) attenuates the exercise-induced
increase in satellite cell numbers and thereby hampers skeletal muscle adaptation to
exercise (Mackey et al. 2007). Interestingly, the second game played 72 h after the
first one was associated with a dampened inflammatory reaction and a more
pronounced pro-inflammatory cytokine response. The implications of this
phenomenon during repeated soccer games deserve further attention.
5.3 STUDY STRENGTHS AND LIMITATIONS
The originality of this thesis is the characterisation of physiological changes that
occur in elite female players following two 90-min soccer games conducted as
competitive games. The study was performed during the game season and both
games included well-trained players who had a demanding training and game
schedule. The strength of this study was that the experiment was conducted in an
actual competitive situation mirroring the real physiological and environmental
factors associated with elite female soccer. Additionally, the ability to monitor the
elite players during a period of five days and to standardise several important factors
The physiological impact of soccer on elite... ✍ helena andersson I 53
52
iii) The low-intensity recovery training performed between two games did not
influence the recovery time of the performance parameters, blood physical stress
markers, the restoration of the redox balance or the inflammatory parameters in
elite female players.
iv) Two repeated elite female soccer games induced similar acute changes in the
neuromuscular fatigue parameters (with the exception of CMJ), elevation in
blood physical stress markers and perceived muscle soreness. Similar acute
oxidative stress reactions and recruitment of endogenous antioxidants occurred
after both games. The dietary antioxidants (with the exception of carotenoids),
however, had dissimilar acute recruitment patterns after both games. Dissimilar
inflammatory responses also occurred after the two games, with a marked
damped cytokine response after the second game.
5.2 IMPLICATIONS
In general, the recovery patterns of the soccer-induced changes in neuromuscular
fatigue parameters, physical stress markers, the redox status and inflammatory
parameters indicate that 72 h between two games is an adequate recovery period in
elite female soccer players. An inter-individual variability in the amplitude of soccer-
induced changes in the physiological variables occured and may be related to the
amount of work performed by each player in the field. It is important to highlight
the fact that the game performance (HIR distance and HR) in the second game was
also not affected by the physiological changes imposed by the first game. However,
the fact that CMJ did not recover during the 72-h period after the first game
indicates that a particular attention should be devoted to the training of explosive
force.
Since the amount of HIR distance during the game was correlated to changes in
CK, HIR may be a useful indicator of the stress put on leg muscles during a game
and may help to individualise the recovery period in soccer players.
Low-intensive recovery training performed at 22 and 45 h after the first game did
not accelerate the recovery of neuromuscular fatigue and physical stress markers, the
redox-balance or the inflammatory response in elite female players. The potential
benefits behind the use of this post-game recovery strategy are not supported by our
53
data. Nevertheless, because of the lack of both positive and negative effects on
recovery, it is suggested that low-intensity exercise can be performed in the recovery
period between soccer games without risks of deteriorating performance in
upcoming games.
This thesis demonstrated the effectiveness of the antioxidant systems in elite
female soccer players. Based on our findings, the regular use of antioxidant
supplements in well-trained female athletes may be questionable. It has been shown
that supplementation with vitamin C may inhibit cellular adaptations to exercise
because it prevents the expression of key transcription factors involved in
mitochondrial biogenesis (Gomez-Cabrera et al. 2008a). The use of supplementation
in elite female players may interfere with soccer-induced training adaptations and
should not be recommended.
The strong pro- and anti-inflammatory cytokine response observed after one single
soccer game in the female players might be an important factor involved in the
adaptation to regular training. The use of anti-inflammatory drugs may therefore
interfere with training adaptations. In this respect, it has been suggested that the use
of nonsteroidal anti-inflammatory drugs (NSAIDs) attenuates the exercise-induced
increase in satellite cell numbers and thereby hampers skeletal muscle adaptation to
exercise (Mackey et al. 2007). Interestingly, the second game played 72 h after the
first one was associated with a dampened inflammatory reaction and a more
pronounced pro-inflammatory cytokine response. The implications of this
phenomenon during repeated soccer games deserve further attention.
5.3 STUDY STRENGTHS AND LIMITATIONS
The originality of this thesis is the characterisation of physiological changes that
occur in elite female players following two 90-min soccer games conducted as
competitive games. The study was performed during the game season and both
games included well-trained players who had a demanding training and game
schedule. The strength of this study was that the experiment was conducted in an
actual competitive situation mirroring the real physiological and environmental
factors associated with elite female soccer. Additionally, the ability to monitor the
elite players during a period of five days and to standardise several important factors
54 I The physiological impact of soccer on elite... ✍ helena andersson
54
during the study period further strengthens the conclusions associated with this
work.
Paradoxically, the strength of this thesis may also be regarded as its weakness.
Due to the limited number of players taking part in a soccer game (22 players), there
were relatively few players per recovery group (active, passive). The scientific
literature in the field does, however, highlight the need for data generated during
experiments conducted in real competitive situations. Moreover, our findings are in
line with data generated by other studies reporting the lack of beneficial effects of
active recovery training (Barnett 2006; Gill et al. 2006; Rowsell et al. 2009).
Furthermore, the game performance (measured as mean HR and time >85%
HRpeak) was similar in both games and did not differ between the players in the
active or passive recovery groups. Regardless of the recovery regime, the players
were, thus, able to perform at a high intensity during the second game. This further
supports the finding that active recovery training has no effect on various
physiological systems. Nonetheless, the relative small sample size should be taken
into account when interpreting the data on the effects of recovery training on the
physiological variables measured in this thesis. Moreover, despite that the effects of
active recovery training was evaluated using a large battery of physiological
parameters, the possibility that this recovery strategy might have affected other
parameters not evaluated in this study cannot be excluded.
It is also important to highlight the difficulty of measuring oxidative stress in
plasma. It is rather difficult to detect reactive intermediates directly in vivo because
of their short half-lives and therefore most studies evaluate various stress markers in
plasma, blood or urine (Urso & Clarkson 2003). In general, every assay has its
advantages and disadvantages and no single measurement can adequately describe
oxidative damage (Nikolaidis et al. 2008). It is suggested, therefore, that the use of a
battery of measurements is important to reliably monitor changes in the redox
system (Halliwell & Whiteman 2004). In the present study, the use of several
biomarkers allowed us to highlight the fact that despite lack of change in lipid
peroxidation measured by d-ROMs, the increased in GSSG, the decreased
GSSG:GSH ratio and increased in antioxidant levels all occurred in response to
exercise.
55
5.4 FUTURE DIRECTIONS
In the present thesis several aspects related to changes in neuromuscular fatigue
markers, the redox-status and inflammatory parameters were revealed for the first
time in elite female soccer players. This provides a platform for future experiments
aimed at further understanding the physiological changes associated with elite female
soccer. International soccer tournaments may include up to six consecutive games.
The implications of our findings in such a situation, where several consecutive games
are separated by only short recovery periods, remain to be elucidated. The context of
international tournaments may also include other important parameters that may
affect the recovery process after a game, including warm and humid climates,
nutritional aspects and psychological factors. The influence of these aspects on
recovery deserves further attention.
Interestingly, CMJ did not recover during the 72-h recovery period after the first
game. There are only a few studies that have investigated the recovery pattern of
performance parameters following soccer games. Furthermore, there are conflicting
results regarding the recovery of CMJ. The understanding of the mechanisms behind
the slow recovery of CMJ in elite female players merits further investigations.
The dampened cytokine response observed following the second game also merits
further attention. It has previously been shown that several immunological
parameters were suppressed for several days after two consecutive games in young
male players (Malm et al. 2004). The implications of the dampened cytokine
response when athletes play multiple soccer games in tournaments are unknown.
Future investigations should also determine whether other forms of recovery
strategies are able to accelerate the recovery of neuromuscular fatigue and blood
physical stress markers, the redox-status and the inflammatory response in elite
soccer players.
The physiological impact of soccer on elite... ✍ helena andersson I 55
54
during the study period further strengthens the conclusions associated with this
work.
Paradoxically, the strength of this thesis may also be regarded as its weakness.
Due to the limited number of players taking part in a soccer game (22 players), there
were relatively few players per recovery group (active, passive). The scientific
literature in the field does, however, highlight the need for data generated during
experiments conducted in real competitive situations. Moreover, our findings are in
line with data generated by other studies reporting the lack of beneficial effects of
active recovery training (Barnett 2006; Gill et al. 2006; Rowsell et al. 2009).
Furthermore, the game performance (measured as mean HR and time >85%
HRpeak) was similar in both games and did not differ between the players in the
active or passive recovery groups. Regardless of the recovery regime, the players
were, thus, able to perform at a high intensity during the second game. This further
supports the finding that active recovery training has no effect on various
physiological systems. Nonetheless, the relative small sample size should be taken
into account when interpreting the data on the effects of recovery training on the
physiological variables measured in this thesis. Moreover, despite that the effects of
active recovery training was evaluated using a large battery of physiological
parameters, the possibility that this recovery strategy might have affected other
parameters not evaluated in this study cannot be excluded.
It is also important to highlight the difficulty of measuring oxidative stress in
plasma. It is rather difficult to detect reactive intermediates directly in vivo because
of their short half-lives and therefore most studies evaluate various stress markers in
plasma, blood or urine (Urso & Clarkson 2003). In general, every assay has its
advantages and disadvantages and no single measurement can adequately describe
oxidative damage (Nikolaidis et al. 2008). It is suggested, therefore, that the use of a
battery of measurements is important to reliably monitor changes in the redox
system (Halliwell & Whiteman 2004). In the present study, the use of several
biomarkers allowed us to highlight the fact that despite lack of change in lipid
peroxidation measured by d-ROMs, the increased in GSSG, the decreased
GSSG:GSH ratio and increased in antioxidant levels all occurred in response to
exercise.
55
5.4 FUTURE DIRECTIONS
In the present thesis several aspects related to changes in neuromuscular fatigue
markers, the redox-status and inflammatory parameters were revealed for the first
time in elite female soccer players. This provides a platform for future experiments
aimed at further understanding the physiological changes associated with elite female
soccer. International soccer tournaments may include up to six consecutive games.
The implications of our findings in such a situation, where several consecutive games
are separated by only short recovery periods, remain to be elucidated. The context of
international tournaments may also include other important parameters that may
affect the recovery process after a game, including warm and humid climates,
nutritional aspects and psychological factors. The influence of these aspects on
recovery deserves further attention.
Interestingly, CMJ did not recover during the 72-h recovery period after the first
game. There are only a few studies that have investigated the recovery pattern of
performance parameters following soccer games. Furthermore, there are conflicting
results regarding the recovery of CMJ. The understanding of the mechanisms behind
the slow recovery of CMJ in elite female players merits further investigations.
The dampened cytokine response observed following the second game also merits
further attention. It has previously been shown that several immunological
parameters were suppressed for several days after two consecutive games in young
male players (Malm et al. 2004). The implications of the dampened cytokine
response when athletes play multiple soccer games in tournaments are unknown.
Future investigations should also determine whether other forms of recovery
strategies are able to accelerate the recovery of neuromuscular fatigue and blood
physical stress markers, the redox-status and the inflammatory response in elite
soccer players.
56 57
6 ACKNOWLEDGEMENTS
This thesis was performed at the School of Health and Medical Sciences, Örebro
University, Sweden. Collaborating centers included the Norwegian School of Sport
Sciences, Oslo; the Department of Nutrition, Institute of Medical Sciences, University
of Oslo; and Olympiatoppen, Oslo, Norway. The studies were funded by the
Swedish National Centre for Research in Sports.
I wish to express my warmest gratitude to all those who contributed to the studies
and made this thesis possible. I would especially like to thank:
Fawzi Kadi, my supervisor, for making my journey as a Ph.D. student a great
learning experience. I am astonished by your knowledge, work capacity, tremendous
patience and humble personality. I admire your courage for taking me on as a
student without knowing me. I am deeply grateful for the expertise, support and
encouragement you have given me during this time, wherever in the world I have
been. I am appreciative to have learnt the research process from the best!
Truls Raastad, my co-supervisor, for the tremendous support and excellent
knowledge. I am especially thankful for your help and hard work with the study set-
up and the data collection; it was a fun week with a lot of hard work. I am also
grateful for your support during difficult times; you always calm me down in stormy
weather!
Karin Söderlund, my co-supervisor, for giving me great advice not only on research
but about life in general. I admire your knowledge and love for science.
My colleagues in Norway for their tremendous help and hard work: Gøran Paulsen,
Anette Karsten, Siv Kjølsrud Bøhn, Rune Blomhoff, Johnny Nilsson, Nils Helge
Kvamme, Einar Sigmundson and Kenneth Wilsgård.
My colleagues who inspired me to commence research in football: Peter Krustrup
and Magni Mohr for believing in me and my ideas and for being good friends; Jens
Bangsbo for great inspiration; H-C Holmberg for pushing me in the right direction;
Paul Balsom for believing in me, encouraging me and guiding me to where I am
today; Barry Drust and Marcus Svensson for great support and good friendship.
The physiological impact of soccer on elite... ✍ helena andersson I 57
56 57
6 ACKNOWLEDGEMENTS
This thesis was performed at the School of Health and Medical Sciences, Örebro
University, Sweden. Collaborating centers included the Norwegian School of Sport
Sciences, Oslo; the Department of Nutrition, Institute of Medical Sciences, University
of Oslo; and Olympiatoppen, Oslo, Norway. The studies were funded by the
Swedish National Centre for Research in Sports.
I wish to express my warmest gratitude to all those who contributed to the studies
and made this thesis possible. I would especially like to thank:
Fawzi Kadi, my supervisor, for making my journey as a Ph.D. student a great
learning experience. I am astonished by your knowledge, work capacity, tremendous
patience and humble personality. I admire your courage for taking me on as a
student without knowing me. I am deeply grateful for the expertise, support and
encouragement you have given me during this time, wherever in the world I have
been. I am appreciative to have learnt the research process from the best!
Truls Raastad, my co-supervisor, for the tremendous support and excellent
knowledge. I am especially thankful for your help and hard work with the study set-
up and the data collection; it was a fun week with a lot of hard work. I am also
grateful for your support during difficult times; you always calm me down in stormy
weather!
Karin Söderlund, my co-supervisor, for giving me great advice not only on research
but about life in general. I admire your knowledge and love for science.
My colleagues in Norway for their tremendous help and hard work: Gøran Paulsen,
Anette Karsten, Siv Kjølsrud Bøhn, Rune Blomhoff, Johnny Nilsson, Nils Helge
Kvamme, Einar Sigmundson and Kenneth Wilsgård.
My colleagues who inspired me to commence research in football: Peter Krustrup
and Magni Mohr for believing in me and my ideas and for being good friends; Jens
Bangsbo for great inspiration; H-C Holmberg for pushing me in the right direction;
Paul Balsom for believing in me, encouraging me and guiding me to where I am
today; Barry Drust and Marcus Svensson for great support and good friendship.
58 I The physiological impact of soccer on elite... ✍ helena andersson
58
My role models, Pia Sundhage and Marika Domanski-Lyfors, who have encouraged
me to continue my Ph.D. even in tough times. I am amazed by your strength and
love for the game. I am forever grateful to you, Pia, for making my passion and
knowledge in soccer even greater; and to you Marika for teaching me never to give
up, no matter what happens. Thank you both for giving me the opportunity to work
with you and experience memories for life. You guys are awesome!
The work colleagues and Ph.D. students in Sport Science at Örebro University for
their support and friendship. Special thanks to Henrik Gustavsson and Mattias
Johansson for many kilometers in the running track and late nights in the
“appendix” discussing life; to Sören Hjälm, John Jouper, Helena Ragnarsson, Anette
Oskarsson and Anita Cierzniewski for making my life easier by being such good
friends.
My friends, Terese Petrone, Charlotte Stichter, Karin Berntsson, Anna Ericsson,
Jovin Lew, Kristina Nygren, Cecilia Pettersson, Erica Lång and Ann-Sofie Flodin for
your great friendship and for taking me out enjoying life between times of hard work.
The players who participated in the study for your patience during the study and for
many good laughs together. I admire your love for the game and the number of
hours you spend training and playing. You made this study possible!
My brother Tomas for tremendous support together with his family Therese, Nils,
Otto and Axel for many joyful times - reminding me that there are other things in
life than work.
My mother and father, Berit and Gunnar, for giving me the assurance I have needed
and for always supporting my choices in life. Your love and support are invaluable.
59
SVENSK SAMMANFATTNING
INTRODUKTION: Damfotboll har blivit mer populär och mer professionell
runtom i världen. Det finns emellertid lite vetenskaplig data om hur
matchbelastningen påverkar fysiologiska parametrar för elitdamfotbollspelare. I
internationella turneringar är det dessutom få dagar mellan matcher och effektiv
återhämtning är viktig för spelarna. Syftet med denna avhandling var därför att
studera fysiologiska förändringar som sker efter matcher i en så verklig situation som
möjligt för elitspelare. Akuta och efterföljande fysiologiska förändringar undersöktes
i samband med två fotbollsmatcher, liksom effekten av aktiv återhämtningsträning
eller passiv vila på återhämtningsförmågan i perioden mellan matcherna.
METOD: Två elitdamfotbollslag spelade två 90-min matcher med 72 tim mellanrum
och som innehöll aktiv återhämtningsträning eller passiv vila. Den aktiva
återhämtningsträningen (cykling 60% av HRpeak och lågintensiv styrketräning på
<50% 1RM) varade i en tim och utfördes dagarna mellan matcherna. De fysiska
mätningarna, countermovementhopp (CMJ), 20–m sprint, maximal isokinetisk knä-
flexionen och extension, mättes före, direkt efter och 5, 21, 45, 51 och 69 tim efter
den första matchen och direkt efter den andra matchen. I blodet mättes fysiska
stressmarkörer (t ex. CK, urea), oxidativa stressmarkörer (t ex. GSSG,
lipidperoxidation), endogena (t ex. urinsyra, thiols) och dietära antioxidanter (t ex.
tocopheroler, karotenoider) samt ett stort batteri av cytokiner (inklusive IL-6 och
TNF-).
RESULTAT: Inga signifikanta skillnader observerades mellan den aktiva och passiva
återhämtningsgruppen i de olika parametrarna. Direkt efter båda matcherna
observerades försämringar med liknande amplitud i sprintförmåga, maximal
isokinetisk knäextension och flexion. CMJ försämrades direkt efter den första
matchen och var reducerad under hela undersökningsperioden. Direkt efter båda
matcherna observerades ökningar med liknande amplitud i plasma CK, urea, uric
syra, FRAP, GSSG, TGSH, leukocyter och neutrophiler samt oförändrad lipid
peroxidation. De dietära antioxidanterna visade antingen en akut och långvarig
förändring (tocopheroler, AA och polyphenoler) eller en fördröjd ökning
(karotenoider) efter den första matchen. En signifikant, men snabbt övergående
ökning av flera pro-inflammatoriska (IL-12, INF-, IL-17, MCP-1, IL-8 och MIG),
anti-inflammatoriska (IL-2R, IL-4, IL-5, IL-7, IL-10, IL-13, INF-) cytokiner och IL-
The physiological impact of soccer on elite... ✍ helena andersson I 59
58
My role models, Pia Sundhage and Marika Domanski-Lyfors, who have encouraged
me to continue my Ph.D. even in tough times. I am amazed by your strength and
love for the game. I am forever grateful to you, Pia, for making my passion and
knowledge in soccer even greater; and to you Marika for teaching me never to give
up, no matter what happens. Thank you both for giving me the opportunity to work
with you and experience memories for life. You guys are awesome!
The work colleagues and Ph.D. students in Sport Science at Örebro University for
their support and friendship. Special thanks to Henrik Gustavsson and Mattias
Johansson for many kilometers in the running track and late nights in the
“appendix” discussing life; to Sören Hjälm, John Jouper, Helena Ragnarsson, Anette
Oskarsson and Anita Cierzniewski for making my life easier by being such good
friends.
My friends, Terese Petrone, Charlotte Stichter, Karin Berntsson, Anna Ericsson,
Jovin Lew, Kristina Nygren, Cecilia Pettersson, Erica Lång and Ann-Sofie Flodin for
your great friendship and for taking me out enjoying life between times of hard work.
The players who participated in the study for your patience during the study and for
many good laughs together. I admire your love for the game and the number of
hours you spend training and playing. You made this study possible!
My brother Tomas for tremendous support together with his family Therese, Nils,
Otto and Axel for many joyful times - reminding me that there are other things in
life than work.
My mother and father, Berit and Gunnar, for giving me the assurance I have needed
and for always supporting my choices in life. Your love and support are invaluable.
59
SVENSK SAMMANFATTNING
INTRODUKTION: Damfotboll har blivit mer populär och mer professionell
runtom i världen. Det finns emellertid lite vetenskaplig data om hur
matchbelastningen påverkar fysiologiska parametrar för elitdamfotbollspelare. I
internationella turneringar är det dessutom få dagar mellan matcher och effektiv
återhämtning är viktig för spelarna. Syftet med denna avhandling var därför att
studera fysiologiska förändringar som sker efter matcher i en så verklig situation som
möjligt för elitspelare. Akuta och efterföljande fysiologiska förändringar undersöktes
i samband med två fotbollsmatcher, liksom effekten av aktiv återhämtningsträning
eller passiv vila på återhämtningsförmågan i perioden mellan matcherna.
METOD: Två elitdamfotbollslag spelade två 90-min matcher med 72 tim mellanrum
och som innehöll aktiv återhämtningsträning eller passiv vila. Den aktiva
återhämtningsträningen (cykling 60% av HRpeak och lågintensiv styrketräning på
<50% 1RM) varade i en tim och utfördes dagarna mellan matcherna. De fysiska
mätningarna, countermovementhopp (CMJ), 20–m sprint, maximal isokinetisk knä-
flexionen och extension, mättes före, direkt efter och 5, 21, 45, 51 och 69 tim efter
den första matchen och direkt efter den andra matchen. I blodet mättes fysiska
stressmarkörer (t ex. CK, urea), oxidativa stressmarkörer (t ex. GSSG,
lipidperoxidation), endogena (t ex. urinsyra, thiols) och dietära antioxidanter (t ex.
tocopheroler, karotenoider) samt ett stort batteri av cytokiner (inklusive IL-6 och
TNF-).
RESULTAT: Inga signifikanta skillnader observerades mellan den aktiva och passiva
återhämtningsgruppen i de olika parametrarna. Direkt efter båda matcherna
observerades försämringar med liknande amplitud i sprintförmåga, maximal
isokinetisk knäextension och flexion. CMJ försämrades direkt efter den första
matchen och var reducerad under hela undersökningsperioden. Direkt efter båda
matcherna observerades ökningar med liknande amplitud i plasma CK, urea, uric
syra, FRAP, GSSG, TGSH, leukocyter och neutrophiler samt oförändrad lipid
peroxidation. De dietära antioxidanterna visade antingen en akut och långvarig
förändring (tocopheroler, AA och polyphenoler) eller en fördröjd ökning
(karotenoider) efter den första matchen. En signifikant, men snabbt övergående
ökning av flera pro-inflammatoriska (IL-12, INF-, IL-17, MCP-1, IL-8 och MIG),
anti-inflammatoriska (IL-2R, IL-4, IL-5, IL-7, IL-10, IL-13, INF-) cytokiner och IL-
60 I The physiological impact of soccer on elite... ✍ helena andersson
60
6 observerades efter den första matchen. En klart minskad cytokinrespons
observerades dock efter den andra matchen.
SAMMANFATTNING: Två elitdamfotbollsmatcher ledde till liknande akuta
förändringar i flera fysiologiska parametrar. Den långvariga reduceringen i
hoppförmåga antyder att damfotbollspelare bör träna explosiv styrka. Ökningen av
antioxidanterna i respons till den ökade produktionen av fria radikaler verkar ha
medfört bibehållen redox-balans efter matcherna. Detta antyder att
elitdamfotbollspelare har ett effektivt antioxidantförsvarssystem under matcher. Den
ökade produktionen av både pro- och anti-inflammatoriska cytokiner efter den
första matchen antyder att spelare har en balanserad pro- och anti-inflammatorisk
respons efter en fotbollsmatch. Konsekvenserna av den reducerade cytokinresponsen
efter upprepade matcher är dock okända. Majoriteten av parametrarna i denna
studie var fullt återhämtade innan den andra matchen och spelarnas arbetskapacitet i
den andra matchen påverkades inte av de fysiologiska förändringarna observerade
efter den första matchen. Slutligen, aktiv återhämtningsträning, som genomfördes
dagarna efter en match, påskyndade inte återhämtningsprocessen för
elitdamfotbollspelarna.
61
REFERENCES
Abramson, J. & Salama, G. (1989) Critical sulfhydryls regulate calcium release from sarcoplasmic reticulum. J Bioenerg Biomembr. 21, 283-294.
Aguiló, A., Tauler, P., Fuentespina, E., Tur, J., Córdova, A. & Pons, A. (2005) Antioxidant response to oxidative stress induced by exhaustive exercise. Physiol Behav. 84, 1-7.
Åkerstrom, T., Steensberg, A., Keller, P., Keller, C., Penkowa, M. & Pedersen, B. K. (2005) Exercise induces interleukin-8 expression in human skeletal muscle. J Physiol. 563, 507-516.
Akova, B., Sürmen-Gür, E., Gür, H., Dirican, M., Sarandöl, E. & Küçükoglu, S. (2001) Exercise-induced oxidative stress and muscle performance in healthy women: role of vitamin E supplementation and endogenous oestradiol. Eur J Appl Physiol. 84, 141-147.
Alberti, A., Bolognini, L., Macciantelli, D. & Caratelli, M. (2000) The radical cation of N,N-Diethyl-para-phenylendiamine: a possible indicator of oxidative stress in biological samples. Res Chem Intermed. 26, 253-267.
Andersson, H., Randers, M., Heiner-Møller, A., Krustrup, P. & Mohr, M. (2010) Elite female soccer players perform more high-intensity running when playing in international games compared to domestic league games. J Strength Cond Res. 24, 912-9.
Ascensão, A., Rebelo, A., Oliviera, E., Marques, F., Pereira, L. & Magalhães, J. (2008) Biochemical impact of a soccer match-analysis of oxidative stress and muscle damage markers throughout recovery. Clin Biochem. 41, 841-851.
Asmus, K-D. & Bonifacic, M. (2000) Free radical chemistry. Free radical chemistry. In: Sen, C., Packer, L, Hänninen, O. (ed) Handbook of oxidants and antioxidants in exercise. Elsevier Science, Amsterdam, pp. 1-57.
Avela, J. & Komi, P. V. (1998) Interaction between muscle stiffness and stretch reflex sensitivity after long-term strecth-shortening cycle exercise. Muscle Nerve 21, 1224-1227.
Balsom, P.D., Harridge, S.D., Soderlund, K., Sjodin, B. & Ekblom, B. (1993) Creatine supplementation per se does not enhance endurance exercise performance. Acta Physiol Scand. 149, 521-523.
Banfi, G., Malavazos, A., Iorio, E., Dolci, A., Doneda, L., Verna, R. & Corsi, M. (2006) Plasma oxidative stress biomarkers, nitric oxide and heat shock protein 70 in trained elite soccer players. Eur J Appl Physiol. 96, 483-486.
Bangsbo, J. (1994) The physiology of soccer - with special reference to intense intermittent exercise. Acta Physiol Scand Suppl. 619, 1-155.
Barnett, A. (2006) Using Recovery Modalities between Training Sessions in Elite Athletes: Does it help? Sports Med. 36, 781-796.
Benzie, I. & Strain, J. (1999) Ferric reducing/antioxidant power assay: direct measure of total antioxidant activity of biological fluids and modified version for simultaneous measurement of total antioxidant power and ascorbic acid concentration. Methods Enzymol. 299, 15-27.
Bishop, N., Gleeson, M., Nicholas, C. & Ali, A. (2002) Influence of carbohydrate supplementation on plasma cytokine and neutrophil degranulation responses to high intensity intermittent exercise. Int J Sport Nutr Exerc Metab. 12, 145-156.
The physiological impact of soccer on elite... ✍ helena andersson I 61
60
6 observerades efter den första matchen. En klart minskad cytokinrespons
observerades dock efter den andra matchen.
SAMMANFATTNING: Två elitdamfotbollsmatcher ledde till liknande akuta
förändringar i flera fysiologiska parametrar. Den långvariga reduceringen i
hoppförmåga antyder att damfotbollspelare bör träna explosiv styrka. Ökningen av
antioxidanterna i respons till den ökade produktionen av fria radikaler verkar ha
medfört bibehållen redox-balans efter matcherna. Detta antyder att
elitdamfotbollspelare har ett effektivt antioxidantförsvarssystem under matcher. Den
ökade produktionen av både pro- och anti-inflammatoriska cytokiner efter den
första matchen antyder att spelare har en balanserad pro- och anti-inflammatorisk
respons efter en fotbollsmatch. Konsekvenserna av den reducerade cytokinresponsen
efter upprepade matcher är dock okända. Majoriteten av parametrarna i denna
studie var fullt återhämtade innan den andra matchen och spelarnas arbetskapacitet i
den andra matchen påverkades inte av de fysiologiska förändringarna observerade
efter den första matchen. Slutligen, aktiv återhämtningsträning, som genomfördes
dagarna efter en match, påskyndade inte återhämtningsprocessen för
elitdamfotbollspelarna.
61
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Aguiló, A., Tauler, P., Fuentespina, E., Tur, J., Córdova, A. & Pons, A. (2005) Antioxidant response to oxidative stress induced by exhaustive exercise. Physiol Behav. 84, 1-7.
Åkerstrom, T., Steensberg, A., Keller, P., Keller, C., Penkowa, M. & Pedersen, B. K. (2005) Exercise induces interleukin-8 expression in human skeletal muscle. J Physiol. 563, 507-516.
Akova, B., Sürmen-Gür, E., Gür, H., Dirican, M., Sarandöl, E. & Küçükoglu, S. (2001) Exercise-induced oxidative stress and muscle performance in healthy women: role of vitamin E supplementation and endogenous oestradiol. Eur J Appl Physiol. 84, 141-147.
Alberti, A., Bolognini, L., Macciantelli, D. & Caratelli, M. (2000) The radical cation of N,N-Diethyl-para-phenylendiamine: a possible indicator of oxidative stress in biological samples. Res Chem Intermed. 26, 253-267.
Andersson, H., Randers, M., Heiner-Møller, A., Krustrup, P. & Mohr, M. (2010) Elite female soccer players perform more high-intensity running when playing in international games compared to domestic league games. J Strength Cond Res. 24, 912-9.
Ascensão, A., Rebelo, A., Oliviera, E., Marques, F., Pereira, L. & Magalhães, J. (2008) Biochemical impact of a soccer match-analysis of oxidative stress and muscle damage markers throughout recovery. Clin Biochem. 41, 841-851.
Asmus, K-D. & Bonifacic, M. (2000) Free radical chemistry. Free radical chemistry. In: Sen, C., Packer, L, Hänninen, O. (ed) Handbook of oxidants and antioxidants in exercise. Elsevier Science, Amsterdam, pp. 1-57.
Avela, J. & Komi, P. V. (1998) Interaction between muscle stiffness and stretch reflex sensitivity after long-term strecth-shortening cycle exercise. Muscle Nerve 21, 1224-1227.
Balsom, P.D., Harridge, S.D., Soderlund, K., Sjodin, B. & Ekblom, B. (1993) Creatine supplementation per se does not enhance endurance exercise performance. Acta Physiol Scand. 149, 521-523.
Banfi, G., Malavazos, A., Iorio, E., Dolci, A., Doneda, L., Verna, R. & Corsi, M. (2006) Plasma oxidative stress biomarkers, nitric oxide and heat shock protein 70 in trained elite soccer players. Eur J Appl Physiol. 96, 483-486.
Bangsbo, J. (1994) The physiology of soccer - with special reference to intense intermittent exercise. Acta Physiol Scand Suppl. 619, 1-155.
Barnett, A. (2006) Using Recovery Modalities between Training Sessions in Elite Athletes: Does it help? Sports Med. 36, 781-796.
Benzie, I. & Strain, J. (1999) Ferric reducing/antioxidant power assay: direct measure of total antioxidant activity of biological fluids and modified version for simultaneous measurement of total antioxidant power and ascorbic acid concentration. Methods Enzymol. 299, 15-27.
Bishop, N., Gleeson, M., Nicholas, C. & Ali, A. (2002) Influence of carbohydrate supplementation on plasma cytokine and neutrophil degranulation responses to high intensity intermittent exercise. Int J Sport Nutr Exerc Metab. 12, 145-156.
62 I The physiological impact of soccer on elite... ✍ helena andersson 62
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neutrophils and E-selectin during early recovery. Can J Appl Physiol. 26, 245-253.
Polman, R., Walsh, D., Bloomfield, J. & Nesti, M. (2004) Effective conditioning of female soccer players. J Sports Sci. 22, 191-203
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The physiological impact of soccer on elite... ✍ helena andersson I 69 68
Reilly, T. & Rigby, M. (1999) Effect of an active warm down following competitive soccer In: Spinks, W., Reilly, T. & Murphy, A. (eds) Science and Football IV, Routledge, pp. 226-229.
Rhodes, E. & Mosher, R. (1992) Aerobic and anaerobic characteristics of elite female university players. J Sports Sci. 10, 143-144.
Richheimer, S., Kent, M. & Bernart, M. (1994) Reversed-phase high-performance liquid chromatographic method using a pentafluorophenyl bonded phase for analysis of tocopherols. J Chromatogr A. 677, 75-80.
Rowsell, G., Coutts, A., Reaburn, P. & Hill-Haas, S. (2009) Effects of cold-water immersion on physical performance between successive matches in high-performance junior male soccer players. J Sport Sci. 27, 565-573.
Sakhi, A. K., Russnes, K. M., Smeland, S., Blomhoff, R. & Gundersen, T. E. (2006) Simultaneous quantification of reduced and oxidized glutathione in plasma using a two-dimensional chromatographic system with parallel porous graphitized carbon columns coupled with fluorescence and coulometric electrochemical detection. J Chromatogr A. 1104, 179-189.
Saltin, B. & Åstrand, P. (1967) Maximal oxygen uptake in athletes. J Appl Physiol. 23, 353-358.
Sastre, J., Asensi, M., Gasgo, E., Pallardo, F., Ferrero, J., Furukawa, T. & Vina, J. (1992) Exhaustive physical exercise causes oxidation of glutathione status in blood: prevention by antioxidant administration. Am J Physiology. 263, R992-R995.
Sen, C.K. & Packer, L. (2000) Thiol homeostasis and supplements in physical exercise. Am J Clin Nutr. 72, 653-669.
Shephard, R. (2002) Cytokine responses to physical activity, with particular references to IL-6: sources, actions, and clinical implications. Crit Rev Immunol. 22, 165-182.
Siegler, J., Gaskill, S. & Ruby, B. (2003) Changes evaluated in soccer-specific power endurance either with or without a 10-week, in-season, intermittent, high-intensity training. J Strength Cond Res. 17, 379-387.
Steensberg, A., Fischer, C., Keller, C., Møller, K. & Pedersen, B.K. (2003) IL-6 enhances plasma IL-1ra, IL-10, and cortisol in humans. Am J Physiol Endocrinol Metab. 285, E433-437.
Stølen, T., Chamari, K., Castagna, C. & Wisløff, U. (2005) Physiology of soccer: an update. Sports Med. 35, 501-536.
Subczynski, W., Markowska, E. & Sielewiesiuk, J. (1991) Effect of polar carotenoids on the oxygen diffusion-concentration product in lipid bilayers. An EPR spin label study. Biochim Biophys Acta. 1068, 68-72.
Sureda, A., Ferrer, M., Tauler, P., Romaguera, D., Drobnic, F., Pujol, P., Tur, J. & Pons, A. (2009) Effects of exercise intensity on lymphocyte H2O2 production and antioxidant defences in soccer players. Br J Sports Med. 43, 186-190.
Suzuki, K., Totsuka, M., Nakaji, S., Yamada, M., Kudoh, S., Liu, Q., Sugawara, K., Yamaya, K. & Sato, K. (1999) Endurance exercise causes interaction among stress hormones, cytokines, neutrophil dynamics, and muscle damage. J Appl Physiol. 87, 1360-1367.
Suzuki, K., Yamada, M., Kurakake, S., Okamura, N., Yamaya, K., Liu, Q., Kudoh, S., Kowatari, K., Nakaji, S. & Sugawara, K. (2000) Circulating cytokines and hormones with immunosuppressive but neutrophil-priming
69
potentials rise after endurance exercise in humans. Eur J Appl Physiol. 81, 281-287.
Svenska Fotbollförbundet (2008) Verksamhetsberättelse, Stockholm, p. 62. Tamer, K., Gunay, G., Tiryaki, G., Cicioolu, I. & Erol, E. (1997) Physiological
characteristics of Turkish female soccer players. In: Reilly, T., Bangsbo, J. & Hughes, M. (eds) Science and Football III. E & Spon, London, pp. 37-39.
Tauler, P., Aguiló, A., Guix, P., Jiménez, F., Villa, G., Tur, J. A., Córdova, A. & Pons, A. (2005) Pre-exercise antioxidant enzyme activities determine the antioxidant enzyme erythrocyte response to exercise. J Sports Sci. 23, 5-13.
Tessitore, A., Meeusen, R., Pagano, R., Benevenuti, C., Tiberi, M., Capranica, L. (2008) Effectiveness of active versus passive recovery strategies after futsal games. Strength Cond Res. 22, 1402-1412.
Todd, M., Scott, D. & Chisnall, J. (2002) Fitness characteristics of English female soccer players: an analysis by position and playing standard. In: Spinks, W., Reilly, T. & Murphy, A. (eds) Science and Football IV. E & Spon, London, pp. 374-381.
Tumilty, D. & Darby, S. (1992) Physiological characteristics of female soccer players. J Sports Sci. 10, 144.
Urso, M. & Clarkson, P. (2003) Oxidative stress, exercise and antioxidant supplementation. Toxicology 189, 41-54.
Vaile, J., Halson, S., Gill, N. & Dawson, B. (2008a) Effect of hydrotheraphy on the signs and symptoms of delayed onset muscle soreness. Eur J Appl Physiol. 102, 447-455.
Vaile, J., Halson, S., Nicholas, G. & Dawson, B. (2008b) Effect of cold water immersion on repeat cycling performance and thermoregulation in the heat. J Sports Sci. 26, 431-440.
Vassilakopoulos, T., Karatza, M.-H., Katsaounou, P., Kollintza, A., Zakynthinos, S. & Roussos, C. (2003) Antioxidants attenuate the plasma cytokine response to exercise in humans. J Appl Physiol. 94, 1025-1032.
Viru, A. & Viru, M. (2001) Biochemical Monitoring of Sport Training. Human Kinetics, Champaign, IL.
Warren, G., Ingalls, C., Lowe, D. & Armstrong, R. (2001) Excitation-contraction uncoupling: major role in contraction-induced muscle injury. Exerc Sport Sci Rev. 29, 82-87.
Warren, G. L., O'Farrell, L., Summan, M., Hulderman, T., Mishra, D., Luster, M. I., Kuziel, W. A. & Simeonova, P. P. (2004) Role of CC chemokines in skeletal muscle functional restoration after injury. Am J Physiol Cell Physiol. 286, C1031-1036.
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Westerblad, H., David, A. & Lännergren, J. (2002) Muscle Fatigue: Lactic Acid or Inorganic Phosphate the Major Cause? News Physiol Sci. 17, 17-21.
Williamson, D. (1991) Belles of the Ball: The early history of women's football. R&D Associates, Devon.
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