Eur J Appl Physiol (2007) 101:587594 DOI 10.1007/s00421-007-0533-5ORIGINAL ARTICLE

EVects of diVering intensities of static stretching on jump performance

David G. Behm Armin Kibele

Accepted: 16 July 2007 / Published online: 4 August 2007 Springer-Verlag 2007

Abstract Acute bouts of static stretching have beenshown to impair performance. Most published studies haveincorporated static stretching that stressed the muscle(s) tothe point of discomfort (POD). There are very few studiesthat have examined the eVects of submaximal intensity(less than POD) static stretching on subsequent perfor-mance. Ten participants were pre-tested by performing tworepetitions of three diVerent stretches to assess range ofmotion (ROM) and two repetitions each of Wve diVerenttypes of jumps. Following pre-testing, participants werestretched four times for 30 s each with 30 s recovery for thequadriceps, hamstrings and plantar Xexors at 100% (POD),75% and 50% of POD or a control condition. Five minutesfollowing the stretch or control conditions, they were testedpost-stretch with the same stretches and jumps as the pre-test. All three stretching intensities adversely aVected jumpheights. With data collapsed over stretching intensities,there were signiWcant decreases in jump height of 4.6%(P = 0.01), 5.7% (P < 0.0001), 5.4% (P = 0.002), 3.8%(P = 0.009) and 3.6% (P = 0.008) for the drop jump, squatjump, countermovement jump (CMJ) to a knee Xexion of70, CMJ using a preferred jump strategy and short ampli-tude CMJ respectively. An acute bout of maximal or sub-maximal intensity stretching can impair a variety ofjumping styles and based on previous research, it is hypoth-esized that changes in muscle compliance may play a role.

Keywords Stretch shortening cycle Muscle compliance Drop jump Countermovement jump Flexibility

Introduction

It seems fairly clear from the recent literature that staticstretching prior to an athletic performance can result in deW-cits for force (Behm et al. 2001; Fowles et al. 2000; Kokko-nen et al. 1998), jump height (Cornwell et al. 2002; Youngand Behm 2003; Young and Elliott 2001) muscle activationas measured by electromyography (Behm et al. 2001; Poweret al. 2004; Rosenbaum and Hennig 1995) and the interpo-lated twitch technique (Behm et al. 2001; Power et al.2004), reaction and movement time and balance (Behmet al. 2004). When jump heights have not been signiWcantlyaVected by static stretching, ground contact times have beenprolonged (Power et al. 2004). These deleterious eVectshave been shown to endure for at least 2 h post-stretching(Power et al. 2004). Even when combined with an aerobicwarm-up (Behm et al. 2001, 2004; Power et al. 2004) andskill rehearsal (Young and Behm 2003), static stretchingexerted negative inXuences upon subsequent performance.These adverse eVects are persistently demonstrated withboth Xexibility trained and untrained individuals (Behmet al. 2006). However, all the aforementioned studies incor-porated static stretching that stressed the muscle groups tothe point of discomfort (POD). There are very few studiesthat have examined the eVects of submaximal intensity (lessthan POD) static stretching on subsequent performance.

Young et al. (2006) recently identiWed a volume and inten-sity eVect to their stretching regime. A greater duration ofstretching resulted in greater deWcits. In addition, staticstretching at 90% of POD provided increases in range ofmotion (ROM) with no deleterious jump performance eVects.

D. G. Behm (&)School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. Johns , NF, Canada A1C 5S7e-mail: dbehm@mun.ca

A. KibeleInstitute for Sports and Sport Science, University at Kassel, Kassel 34121, Germany123

588 Eur J Appl Physiol (2007) 101:587594Knudson and colleagues published two studies (Knudsonet al. 2001, 2004) where the subjects were stretched to a pointjust before discomfort. Neither study showed signiWcantdecreases in performance. With respect to the very limitedinformation regarding submaximal intensity static stretching,it would be important to elaborate on the eVects of submaxi-mal intensity static stretching on dynamic jump activities.Furthermore, it is also important to establish whether moder-ate (i.e. 75% of POD) or lower intensity (i.e. 50% of POD)static stretching would result in stretch-induced impairments.

Thus, the objective of this study was to determine theextent of changes in various parameters of jump perfor-mance that could occur with static stretching at 100, 75 and50% of POD. It was hypothesized that the lowest intensity-stretching regimen (50%) would provide increases in ROMwithout detrimental eVects on jump performance.

Methods

Experimental design

After warming up on a cycle ergometer, participantswere pre-tested by performing two repetitions of three

diVerent stretches to assess ROM and two repetitionseach of Wve diVerent types of jumps. Following pre-test-ing, participants were stretched four times for 30 s eachwith 30 s recovery for the quadriceps, hamstrings andplantar Xexors at 100% (POD), 75% of POD and 50% ofPOD or a control condition. Five minutes following thestretch or control conditions, they were tested post-stretch with the same stretches and jumps as the pre-test(Fig. 1). The diVering intensities of stretch (100% (POD),75% of POD and 50% of POD and control) were per-formed on separate days with at least 48 h rest betweensessions.

Participants

A sample group of convenience consisting of ten partici-pants (7 males; age = 27.6 3.7 years, height = 180.6 2.5 cm, mass = 77.1 5.7 kg and 3 females; age = 24.0 0.8 years, height = 169.7 1.2 cm, mass = 58.7 4.8 kg) participated in the study. All participants were froma university student population. Each subject was requiredto read and sign a consent form prior to participating in thestudy. The institutions Human Investigations Committeeapproved the study.

Fig. 1 A diagrammatic repre-sentation of the experimental design

5 min cycle ergometer warm-up at 70 Watts

Pre-stretch Tests

Stretches1) Stoop and Reach

2) Supine Hip Flexion with Knee Extended 3) Prone Hip Extension with Knee Extended

Jumps1) 24 cm drop jump

2) CMJ with fast SSC 3) CMJ with slow SSC to 70 knee flexion

4) Self selected (pace and depth) CMJ 5) Concentric-only squat jump

Stretch Conditions1) 100% of point of discomfort (POD) 2) 75% of POD 3) 50% of POD 4) Control (5 s stretch at maximal POD)

Stretches 4 stretches of 30 s each with 30 s recovery

1) Unilateral kneeling knee flexion (quadriceps), 2) Supine hip flexion with extended knee (hamstrings) 3) Ankle dorsiflexion while standing upright on an elevated platform (stretch of the plantar flexors with soleus emphasis)

5 min following stretch intervention Post-stretch Tests

Stretches1) Stoop and Reach

2) Supine Hip Flexion with Knee Extended 3) Prone Hip Extension with Knee Extended

Jumps1) 24 cm drop jump

2) CMJ with fast SSC 3) CMJ with slow SSC to 70

knee flexion 4) Self selected CMJ (pace and depth)

5) Concentric-only squat jump 123

Eur J Appl Physiol (2007) 101:587594 589Dependent variables

All participants warmed up on a cycle ergometer (Monark;Ergomedic 828E) at 70 rpm with a resistance of 1 kp(70 Watts) for 5 min. ROM tests were performed in a ran-dom order with two repetitions of three stretches. Stretchtests included a standing stoop and reach where an individ-ual stood on an elevated platform and with knees fullyextended reached downwards as far as possible. The dis-tance from or past the platform was noted. A plastic goni-ometer was used to measure the ROM when performing asupine hip Xexion movement with knee fully extended(Canadian Society for Exercise Physiology 2003). The thirdstretch test had the participants prone on the mat, wherethey attempted to extend their hip with knee fully extended.The distance from the mat to the patella was measured incentimetres (Canadian Society for Exercise Physiology2003). Immediately following the stretch testing, jump testswere conducted. All stretch and jump tests were repeatedbefore and following the stretch intervention.

Five types of jump tests were executed on a Kistler forceplate (type 9281, Kistler Instrument Corp., Amherst, NY,USA) before and following the static stretching interven-tion. Jump tests included a drop jump from a 24 cm plat-form, concentric only squat jump with knees initiallypositioned at 70, countermovement jump (CMJ) with aslow stretch-shortening cycle (SSC) to a knee Xexion of 70(CMJ 70), CMJ with knee depth and speed self-selectedby the individual (CMJ preferred), and CMJ emphasizing ashort amplitude and high speed SSC of the quadriceps(short amplitude CMJ). For the 24 cm drop jump, partici-pants were instructed to emphasize a short ground contacttime (of about 200 ms) while attempting to achieve thegreatest vertical height (Young and Behm 2003). Knee Xex-ion and extension were minimized during the drop jump bythe instructions and the demonstration by the investigators,which emphasized minimal knee and hip Xexion. Thus withthese instructions, knee Xexion and extension wereexpected to be kept minimal during the drop jump placing agreater emphasis on the SSC of the plantar Xexors. A simi-lar drop jump procedure has been used in a number of stud-ies by Young (Young and Behm 2003, Young et al. 2006).The downward displacement of the center of mass afterlanding from the drop jump was monitored and controlledby a double integration procedure of the force-time recordoutlined by Kibele (1999). The CMJ with a fast SSC (shortamplitude CMJ) emphasized the plantar Xexors and thuswas implemented to compare a rapid SSC of a countermov-ement jump with a rapid SSC drop jump that had an evengreater plantar Xexors emphasis. The CMJ with a slow SSCto 70 allowed a comparison of slow (CMJ 70) and fastSSC (short amplitude CMJ). The CMJ conducted at theindividuals own pace and depth (CMJ preferred) was

instituted to observe stretch-induced changes in jump strat-egy when unimpeded by researcher instructions. Finally theconcentric-only squat jump would provide a comparisonwith the diVerent SSC jumps (CMJ preferred, short ampli-tude CMJ and CMJ 70). To control for the diVerent CMJs,the displacement of the centre of gravity during the down-ward movement was calculated by a double integration pro-cedure of the force-time record outlined by Kibele (1998).All subjects went through an orientation period at least 24 hprior to testing to provide an opportunity to practice thejumps under the supervision of the researcher.

All jumps were performed with hands on hips (akimbo).Two repetitions were performed for each jump with thejump achieving the greatest height used for analysis. One-minute recovery periods were permitted between jumps.The order of jump tests was randomized with one excep-tion. Since the software for the force plate necessitated aninitial body mass to be registered in order to calculate jumpparameters, the testing always began with one of the count-ermovement or concentric only squat jumps. Thus, the dropjumps were never the Wrst test. Post-stretch testing com-menced 5 min following the Wnal stretch intervention.

Independent variables

Immediately following the pre-test, the stretching interven-tion commenced. The order of quadriceps, hamstrings andplantar Xexors stretching was randomized. Based on previ-ous research that recommended 30 s or greater duration ofstretching (Bandy and Irion 1994; Bandy et al. 1997),stretches were held for a duration of 30 s with 30 s recoveryperiods between stretches. Each type of stretch wasrepeated four times. Stretching of both legs included aseries of unilateral kneeling knee Xexion (quadriceps),supine hip Xexion with extended knee (hamstrings), andankle dorsiXexion while standing upright on an elevatedplatform in a step position with the body weight moved tothe rear leg (stretch of the plantar Xexors with gastrocne-mius emphasis) (Alter 1996). Stretching was passive for thequadriceps and hamstrings with the same investigator con-trolling the change in the ROM and resistance for all sub-jects. For the ankle dorsiXexion, subjects moved the bodyweight to the rear leg while executing at 50%, and 75%,and 100% stretch on the calf muscles.

A manual muscle strength tester (Lafayette Instruments)was used to quantify the stress on the limb during stretch-ing. The researcher placed the manual muscle strengthtester against the anterior (quadriceps stretch) or posterior(hamstrings stretch) portion of the limb at the level of themalleoli. The researcher would push against the limb toincrease the ROM until the participant indicated that theyhad reached POD. The force reading at this point wasnoted. For the 100% intensity stretch, this force level would123

590 Eur J Appl Physiol (2007) 101:587594be maintained for the four sets of 30 s stretches. For sub-maximal intensity stretches, the POD force would be main-tained for 5 s or less to establish the force level. Theparticipants limb would then be moved to a ROM thatindicated that the limb was exerting either 75 or 50% of thePOD stretch force upon the manual muscle strength tester.

During the unilateral plantar Xexors stretch, the subjectswere standing upright at the edge of an elevated platform.A step posture was required while subjects pushed the heelof their rear leg beyond the edge of the platform. For the100% intensity condition (POD), full body weight movedtowards the rear leg to the POD. This posture was main-tained for the four sets of 30 s stretches. The POD stretchwas determined on each testing day (condition). For thesubmaximal intensity stretch conditions, subjects wereasked to individually determine a resistance of about 75 or50% loading on the rear leg for approximately 5 s. A nor-mal upright stance with body weight distributed equally onboth feet was considered as reference condition. Visualinspection of the heel displacement below the platform wasused as an estimate for the loading condition. Five minutesfollowing the static stretching intervention, post-teststretches and jumps were conducted.

Since the plantar Xexors were stretched to a subjectiveassumption of 50 or 75% of POD, rather than using theobjective manual muscle tester, it was necessary to evaluatethe reliability of this method. Subjects stood on the plat-form, which was slightly elevated above the Xoor to ensureenough space for a downward displacement of the heel. Thefront foot was slightly forward in a step posture while therear food slightly backward with the middle of the rear footplaced right above the edge of the platform. The heel of therear foot was pushed downward beyond the edge of theplatform by pulling at a cable strain gauge in an upwarddirection. There was force exerted onto the heel through apull on the cable while the plantar Xexors being stretched atthe same time. This force could be read from the digital dis-play of the strain gauge system. Subjects were asked tostretch the plantar Xexors at an estimated intensity of 100%(= POD). Three measures for the 100% condition were con-ducted with 45 min between repetitions. The plantar Xex-ors of the dominant leg (used for unilateral high jumping)were stretched. Ten minutes later, subjects were asked toexecute the stretch with an estimated 50% of the previousstretching force. Again, three repeated measures were eval-uated. No feedback regarding the force values was given tothe subjects. Force values from the strain gauge were regis-tered during each stretch. Intraclass correlations for theforces values were calculated to estimate reliability for the100 and the 50% condition. Three repeated measures wereincluded into the analysis.

The control condition had the participants perform the5 min cycle warm-up. Following the warm-up, they per-

formed all the stretches to the POD for 5 s in order to simu-late the initial stage of the submaximal intensity stretches.They then relaxed for 12 min (control duration similar tothe stretching intervention duration) after the pre-testsbefore being tested again for the post-tests. Each stretch orcontrol condition was allocated in a randomized fashionand performed on separate days.

Statistical analysis

A two way repeated measures ANOVA (4 2) was per-formed to determine if signiWcant diVerences existedbetween conditions (100, 75 and 50% of POD stretches andcontrol) and testing (pre- and post-stretch) data (GB StatDynamic Microsystems, Silver Spring Maryland USA). Analpha level of P = 0.05 was considered statistically signiW-cant. If signiWcant main eVects or interactions were presenta Bonferroni post hoc analysis (GB Stat Dynamic Micro-systems, Silver Spring Maryland USA) was conducted.EVect sizes (ES) were also calculated and reported (Cohen1988). Cohen applied qualitative descriptors for the eVectsizes with ratios of 0.2, 0.5 and 0.8 indicating small, moder-ate and large changes respectively. Descriptive statisticsincluded means standard deviation (SD). Reliability ofthe measurements was assessed with a Cronbach modelintra-class correlation coeYcient (ICC) (McGraw andWong 1996; Vincent 1999) with all subjects.

Results

The day to day reliability (ICC) of force measures using themanual muscle strength testing device to determine thePOD during quadriceps and hamstring stretching wasr = 0.97. For the reliability estimation of the plantar Xexorstretching procedure, the ICC for the estimated 100% con-dition across the three repeated measurements was r = 0.94(with a mean value = 737 N) and for the estimated 50%stretch condition: r = 0.97 (with a mean values = 407 N).Therefore for the 50% condition, subjects were able to pro-duce 53.7% of their maximal forces in the 100% condition.The ICC values for the pre-stretch jump heights whentested repeatedly over all four conditions (100, 75, 50% ofPOD and control) were 0.96, 0.93, 0.91, 0.86 and 0.89 forthe squat jump, CMJ preferred, CMJ 70, CMJ short ampli-tude and drop jump respectively.

There was a signiWcant (P = 0.01) main eVect for timewith a mean 3.5% decrease in all jump height measures(Table 1). The mean data for all stretching intensities com-bined (control condition excluded), indicated signiWcantdecreases in jump height of 5.3% (P = 0.01, ES = 0.22),3.8% (P < 0.0001, ES = 0.36), 5.6% (P = 0.002, ES= 0.35), 3.6% (P = 0.009, ES = 0.26) and 4.6% (P = 0.008,123

Eur J Appl Physiol (2007) 101:587594 591ES = 0.3) for the drop jump, squat jump, CMJ 70, CMJpreferred and short amplitude CMJ, respectively (Fig. 2).There were no signiWcant changes in jump measures withthe control condition over time.

A main eVect for stretching condition was also apparent(P = 0.01). Post-hoc testing indicated there was no signiW-cant diVerence between the three stretching intensities.There were no signiWcant interaction eVects between thestretching conditions (stretching condition x time) indicat-ing that jump heights decreased similarly with 100, 75 and50% of POD stretching (Table 1). There was also no eVectof stretching on the lowering of the centre of gravity priorto jump take-oV.

There was also a tendency (P = 0.06, ES = 0.24) forcontact times with the drop jump to increase by 4.5% (pre-stretch: 223.3 ms 42.1 vs. post-stretch 233.4 ms 45.4).

The Xexibility testing before and after the stretching pro-cedures showed signiWcant diVerences between the warm-up and the post-stretch testing only for the standing stoopand reach. A two way repeated measures ANOVA (4x2) formultivariate tests revealed a signiWcant main eVect for thepre-post measurement (P < 0.05, ES = 0.41), for thestretching condition (P = 0.05, ES = 0.52), and for theinteraction eVect (P < 0.01, ES = 0.86). No signiWcantdiVerences were found for the hip extension and the Xexiontesting. Overall (main eVect), the stoop and reach distanceincreased by 12.1% with the three intensities of stretchingcombined (interaction eVects: 8, 9.7% with 100% POD; 8,13.9% with 75% of POD and 8, 12.6% with 50% of POD).There was no signiWcant diVerence in the stoop and reachwith the control condition.

Discussion

The most interesting Wnding in this study was that all inten-sities of prior static stretching whether submaximal (50 and75% of POD) or maximal (100% of POD) resulted in sig-niWcant impairments in jump height. Previous researchinvolving prior static stretching have resulted in impair-ments of force (Behm et al. 2001; Kokkonen et al. 1998;Fowles et al. 2000), jump height (Young and Behm 2003;

Fig. 2 Main eVect for stretching. Changes in jump height pre- andpost-static stretching with data collapsed over the intensity of stretch-ing (50, 75 and 100% POD data combined). All jump types had signiW-cant decrements (P < 0.01) post-stretching. The control condition didnot experience signiWcant jump impairments and has not been includedin this Wgure. Columns and bars represent means standard deviation

0

5

10

15

20

25

3035

40

Squat Jump

Jum

p He

ight

(cm)

Pre-StretchPost Stretch

CMJ Preferred CMJ 90 CMJ SA DJ

Table 1 Pre- to post-stretch percentage decreases in jump height with the Wve jump variables

100% POD 75% POD 50% POD Control

Drop Jump 3.8 6.1 6.1 1.0Squat Jump 2.4 3.7 5.3 3.6% increaseCountermovement

jump (CMJ) preferred4.2 3.9 2.8 0.7

CMJ 70 5.8 3 8.0 0.9Short amplitude CMJ 4.4 5.4 4.0 0.5Mean 4.1 4.4 5.2 0.1 no signiWcance

Stoop and reach test data

Subjects Stretch test 1 Stretch test 2

1 13.17 13.432 5.23 5.833 6.7 6.574 7.2 5.15 9.37 9.036 5 5.477 4.7 4.58 4.47 6.37

There were no signiWcant diVer-ences between stretch intensities (interactions) but there was a main eVect for stretching overall123

592 Eur J Appl Physiol (2007) 101:587594Young and Elliott 2001; Cornwell et al. 2002), drop jumpground contact times (Behm et al. 2006), muscle activation(Behm et al. 2001; Power et al. 2004; Rosenbaum and Hen-nig 1995), reaction and movement time and balance (Behmet al. 2004). However, all of these studies instituted stretch-ing regimes that had the participants stretch to the POD.There has been some evidence in the literature to suggestthat less than maximal intensity stretching might not pro-duce these deWcits (Young et al. 2006; Knudson et al. 2001,2004).

Young et al. (2006) manipulated the volume of stretch-ing and in one condition had the participants stretch to 90%of POD. The submaximal intensity stretch of the plantarXexors was calculated by decreasing the range of motion by10% from the angle achieved when the subjects werestretched at the POD. They found that 2 min of staticstretching at 90% intensity had no eVect on muscle perfor-mance (concentric calf raise and drop jump height). In thepresent study, the 75 and 50% POD stretches resulted insmaller hip Xexion angles that were 14.8 and 19.4,respectively less than the 100% stretch at the POD.Changes in ankle ROM were not measured. Hence in thepresent study, the submaximal stretching angles were rela-tively comparable or even less than the Young study.DiVerences in jump results between the two studies mayexist since Young and colleagues stretched only the plantarXexors whereas the present study stretched the quadriceps,hamstrings and plantar Xexors. Similar to the volume ofstretch eVects reported in Youngs study (1 min of stretch-ing garnered signiWcantly less jumping impairments than 2or 4 min), the control condition in the present study whoperformed 5 s of maximal static stretching did not experi-ence signiWcant jump height decrements. Knudson and col-leagues published two studies (Knudson et al. 2001, 2004)where the subjects were stretched to a point just beforediscomfort. Neither study showed signiWcant decreases inperformance. In one study (2001) there was a trend towardsimpaired vertical jump height (3%), while the other studyreported no change in tennis serve velocity (2004). Theirsubjective just before discomfort stretch point was notmeasured for ROM and thus it is diYcult to comparebetween the studies.

It was hypothesized in the present study that stretchingto the POD would have greater impairments on perfor-mance than submaximal intensity stretches. High intensity(POD) stretch-induced stress might have a detrimentaleVect of on neuromuscular activation (Avela et al. 1999;Behm et al. 2001; Power et al. 2004). Avela et al. (1999)reported that following 1 h of passive stretching of the tri-ceps surae there were signiWcant decreases in MVC(23.2%), EMG (19.9%), and H-reXex (43.8%). It has beensuggested that the decrease in the excitation of the moto-neuron pool resulted from a reduction in excitatory drive

from the Ia aVerents onto themotoneurons, possibly dueto decreased resting discharge of the muscle spindles viaincreased compliance of the MTU (Avela et al. 1999). Fur-ther inhibitory inXuences on the motoneuron could arisefrom Type III (mechanoreceptor) and IV (nociceptor) aVer-ents (Fowles et al. 2000), However, this decreased excita-tion is more prevalent during the stretch and recoversimmediately after the stretch (Fowles et al. 2000; Guissardet al. 2001).

With stretching to the POD, there is an attempt to Xex orextend to the limit of the individuals joint ROM. KneeXexion during the quadriceps stretch would increase intra-articular knee pressure (Eyring and Murray 1964; Jaysonand Dixon 1970) as well as compress the patella upon thejoint. In addition, dislocating torques would be placed uponthe tibial portion of the knee joint, by forces pulling orpushing the distal portion of the tibia towards the pelvis.Prolonged stress on the joint receptors could possibly leadto inhibitory eVects upon the motoneuron. Similar to otherreXex actions, any inhibitory actions would exert theirgreatest eVects during the stretch period with minimal con-tinuance 510 min into recovery.

In addition to the reported transitory eVects of inhibitoryneural responses, anecdotal reports from the participantsindicated that the stresses placed on the joints and muscleswith the submaximal intensity stretching especially at 50%POD was perceived to be very light. Therefore, it wouldseem unlikely that this intensity of stretching would haveplaced undue stress on the joint receptors, mechanoreceptors,Golgi tendon organs or highly activated the nociceptors.Thus, the evidence seems to indicate that the stresses asso-ciated with stretching to the POD or less are unlikely tolead to prolonged inhibition due to neural inhibition. Thesimilar deWcits irrespective of the stretch intensity in thepresent study might be attributed to similar changes in mus-cle compliance. All stretching intensity protocols in thepresent study signiWcantly increased stoop and reach ROMmeasures by approximately 914%.

An acute bout of stretching has been reported to alter thelength and stiVness of the aVected limb musculotendinousunit (MTU). Although the exact mechanisms responsiblefor increases in ROM following stretching are debatable,the increase has been attributed to decreased MTU stiVness(Wilson et al. 1991, 1992) as well as increased tolerance tostretch (Magnusson et al. 1996a). Studies have reportedboth decreases (Magnusson et al. 1996b; Toft et al. 1989)and no change (Magnusson et al. 1996a, 2000) in MTUpassive resistance or stiVness with an acute bout of stretch-ing.

Changes in MTU stiVness might be expected to impactthe transmission of forces and the rate of force transmis-sion, which are essential variables in the vertical jumpheight. A slacker parallel and series elastic component123

Eur J Appl Physiol (2007) 101:587594 593could increase the electromechanical delay by slowing theperiod between myoWlament crossbridge kinetics and theexertion of tension by the MTU on the skeletal system. Alengthened muscle due to an acute bout of static stretchingcould have a less than optimal cross-bridge overlap which,according to the length tension relationship (Rassier et al.1999), could diminish muscle force output. The elongationof tendinous tissues can also have an eVect on force output(Kawakami et al. 2002). Kokkonen et al. (1998) reported adecrease in 1 RM for the knee extensors and Xexors after anacute bout of passive stretching of both muscle groups for20 min. They suggested that the stretching treatment mighthave inXuenced maximal strength through a reduction ineither the passive or active stiVness of the MTU. Rosen-baum and Hennig (1995) investigated the acute eVects ofprior exercise (warm-up and stretching) on Achilles tendonreXex activity. They found a decrease in the reXexive peakforce and myoelectrical activity of the triceps surae. Addi-tionally, they also found the passive peak force caused by atendon tap to be signiWcantly reduced following the stretch-ing treatment. Decreases in peak twitch torque (poststretch15 min recovery) following prolonged stretchingwere implicated as evidence of impaired muscle contractileforce by Fowles et al. (2000). Since an evoked twitchinvolves an incomplete saturation of the myoWlaments withCa2+ (Binder-MacLeod and Lee 1996), resulting in signiW-cantly less force than an MVC, the dramatically smallerforce of a twitch would be more sensitive to changes inmuscle stiVness. The similar deWcits in vertical jump heightirrespective of stretch intensity would suggest that it is notthe stretch-induced muscle or joint stress that impacts theimpairments, but the increase in muscle compliance pro-vides the most signiWcant impediment.

The data analysis in the present study also indicated thatthere were no changes in the depth of the centre of gravityduring the drop jumps, CMJ preferred and short amplitudeCMJ. Unlike the squat jump and CMJ 70 where the lower-ing of the centre of gravity was controlled, the centre ofgravity depth could be altered in the other jumps. The ratio-nale for measuring the depth of the centre of gravity was toinvestigate whether the neuromuscular system would com-pensate for a more compliant or less stiV MTU by increas-ing the ROM over which force could be exerted. Hence,would the neuromuscular system attempt to increase theamount of work (force distance) or impulse (force time) to achieve similar jump heights? The results of thisstudy indicated that there was no compensatory alterationin the centre of gravity.

Furthermore, the acute stretching eVects did not havespeciWc eVects on the individual jumps whether theyemphasized plantar Xexors SSC (drop jumps), a brief quad-riceps SSC (short amplitude CMJ), slower quadriceps SSC(CMJ 70), self selected quadriceps SSC (CMJ preferred)

or a concentric only squat jump. However, there was atrend (P = 0.06) towards a longer ground contact time withthe drop jump. This Wnding corresponds with Power et al.(2004) who also reported increased ground contact timesduring a drop jump following stretching to the POD. Theysuggested that the increased contact times were further evi-dence of the increased muscle compliance which adverselyaVected force output in their study. Furthermore, Kuboet al. (2007) reported that pre-stretch augmentation withboth CMJ and drop jumps was related to tendon stiVness.Hence, if an acute bout of static stretching whether at maxi-mal or submaximal intensities decreased tendon compli-ance, there could be a signiWcant eVect on jump height asseen in the present study. Increased ground contact timesmay be illustrative of the muscle or tendon compliance-induced impairments to the rate of force transmission ordevelopment.

There were no signiWcant changes in hip Xexion orextension ROM tests following the stretching protocol. Forthe supine hip Xexion measurement, the plastic goniometermust be aligned precisely with the greater trochanter of thefemur and the distal segment of the limb. According toHubley-Kozey (1991), there is considerable diYculty inlocating the true joint centre with this method and aligningthe limbs. Similarly, it is important but also diYcult tomaintain contact of the hip with the mat when performingthe hip extension ROM test (Canadian Society for ExercisePhysiology 2003). Similar diYculties may have increasedthe variability of these measurements in the present study.

The submaximal intensity stretches provided greaterstoop and reach scores than the maximal intensity stretches.Stretches to the maximum POD might cause some minormuscle damage similar to the eVects seen with the eccen-tric-induced damage associated with delayed onset musclesoreness (DOMS). The decreased ROM associated withDOMS has been attributed to an increase in passive tension(Reisman et al. 2005). Alternatively the excessive stretchtension could also elicit greater myotatic stretch reXexactivity increasing the active stiVness of the muscle.

Conclusion

Similar to previous research incorporating acute bouts ofstatic stretching to the point of discomfort, submaximalintensity static stretches in the present study resulted injump height deWcits for all jumps tested. While it is possi-ble there were inhibitory neuromuscular eVects impactingon the jumps, it is hypothesized that changes in musclecompliance played the more signiWcant role in the impair-ments. There were no changes in jump strategy (amplitudeof centre of gravity during eccentric phase) in attempt tocompensate for the static stretching-induced decrements.123

594 Eur J Appl Physiol (2007) 101:587594Therefore, it is recommended that static stretching of anyintensity above 50% of POD should not be conducted priorto an athletic performance attempting to achieve maximumjump heights. Although the statistically signiWcant changesreported in this study were small (3 to 6%), the eVect sizedescriptors of change in magnitude were moderate. Whilethe application of these Wndings may not translate intohighly detectable changes for the sedentary or recreation-ally athletic individual, they could have major conse-quences for the elite athlete for whom impairments of 36% could mean the diVerence between winning and losing.

Acknowledgments This research was supported by a grant from theNational Science and Engineering Research Council (NSERC) ofCanada and by a grant from the University of Kassel.

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EVects of diVering intensities of static stretching on jump performanceAbstractIntroductionMethodsExperimental designParticipantsDependent variablesIndependent variablesStatistical analysis

ResultsDiscussionConclusionReferences

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