temperature regulation during exercise exercise performance & exhaustion heat acclimation
DESCRIPTION
Outline. Temperature Regulation During Exercise Exercise Performance & Exhaustion Heat Acclimation Hydration / Blood Volume. Temperature Regulation During Exercise. Heat Stress & Physiological Temperature Regulation. Gisolfi & Wenger ESSR 1984. Thermoregulatory Control Exercise. - PowerPoint PPT PresentationTRANSCRIPT
• Temperature Regulation During Exercise• Exercise Performance & Exhaustion• Heat Acclimation• Hydration / Blood Volume
Outline
Temperature Regulation During Exercise
Heat Stress & Physiological Temperature Regulation
Gisolfi & Wenger ESSR 1984
Thermal Command
Signal(Load Error)
Set Point Temperature
IntegrateAfferent Signals
Deep Body Temp.
HypothalamicTemp.
Skin Temp.
CoreTemps.
+_
Sweating
Vasodilation
Vasoconstriction
vascular pressures,ions & osmolality,exercise
Thermoregulatory Control Exercise
Sawka et.al. Handbook of Physiology, 1996
Sweating & “Active” Cutaneous Vasodilation
TCSSudomotor
Nerve Sweat Gland
Vasodilation
ACH, VIP
ACH, VIP
TCS
Sudomotor Nerve
Sweat Gland
Vasodilation
ACH
(?)
Non-Thermal
VasodilatorNerve
A.
B.
modified from Johnson & Proppe Handbook of Physiology, 1996
Sweating parallels vascular conductance
Sweating opposite of vascular conductance
(e.g., isometric exercise)
39.5
39.0
38.5
38.0
37.5
37.010 15 20 25 30 35
Core
Tem
pera
ture
(°C)
WBGT (°C)
1000W
500W
350W
200W
Exercise Intensity & Climate Effects on Core Temperature
UncompensableHeat Stress
Compensable Heat Stress
adapted from, Lind et.al JAP 1963
(20 g/min, 1.2 L/h)
(10 g/min, 0.6 L/h)
(7 g/min, 0.4 L/h)
(4 g/min, 0.25 L/h)
Prescriptive Zone
Summary: Temperature Regulation
• Metabolic Rate Dictates Required Heat Loss • Warmer Environment Greater Need for Evaporation• Core Temperature Increase
• Exercise Intensity• Climate
Exercise Performance & Exhaustion
100
90 80
70
60
Environmental Temperature (°C) 4 11 21 31
Tim
e t o
Exh
a ust
ion
(min
)
~10oC (50oF) Optimum Temperature
Heat Stress Reduces Endurance Exercise (~70-75% of VO2max)
Galloway & Maughan, MSSE, 1997
Heat Stress Reduces Maximal Aerobic Power(49oC; 20% RH)
Sawka et al. EJAP 1985
2 3 4 50
5
10
15
20%
Dec
reas
e A
erob
ic P
ower
, Hea
t
VO2 max ( L · min-1) , Temperate
% o
f Sub
ject
s Ex
haus
ted
From
Hea
t Str
ain
0
25
50
75
100
37.0 38.0 39.0 40.0 41.0
Core Temperature (°C)
CompensableHeat Stress(cool skin)
UncompensableHeat Stress
(hot skin)
Core Temperature at Exhaustion from Heat Strain
modified from, Sawka et.al. ESS 2000; Sawka et.al. MSSE 2002
(n = 747)
Maron et.al. EJAP 1977
Cheuvront & Haymes Spts. Med. 2001(n= 776)
Many StudiesOf Trained Athletes
(n = 123)
Core Temperature at Exhaustion: Champion Runners(maximal effort races)
modified from S. Robinson, Pediatrics 1963
0 2010 30Minutes of Running
40
38
39
41C
ore
Tem
pera
ture
(o C)
Ta= 30oCTa= 31oC
Ta= 31oC Ta= 10oC
Why Does Heat Stress Reduce Exercise Performance?
• Circulatory Strain• High Skin Blood Flow, Peripheral Pooling• Stroke Volume, Cardiac Output, Blood Pressure
• Central Nervous System (“Critical Core Temperature”)• Brain EEG & Motor EMG Activity, Voluntary Force Activation• Serotonin (5-HT) Accumulation (Plasma Prolactin)
• Metabolic• Skeletal Muscle Blood Flow • Substrate Utilization / Metabolite Accumulation
Heat Stress Increases Circulatory Strain by Skin Blood Flow / Volume
Rowell Human Circulation 1986
SKBFmax= 7.8 L/min
Critical Core Temperature or Circulatory Strain?
Control Pre-cooling Pre-heating
Time to Exhaustion
(min)
46 63 28
Core Temp. (oC)
40.2 40.1 40.7
Skin Temp.(oC)
37.2 37.2 37.0
Heart Rate(bpm)
197 198 196
Gonzalez-Alonzo et.al., JAP 1999
(60% VO2 max; 40oC)
Brisson et al., JAP, 1991
(45 min cycling (65%VO2max)
Hyperthermia Increases Prolactin, Measure of Central 5-HT Activity
*
41C 10C
PRL
fr
om b
asel
ine
(ng/
ml)
50
40
20
10
0Ambient Temperature
Tc >38oC
Time (s)0 30 60 90 120
Volu
ntar
y ac
tivat
ion
perc
enta
ge
0
40
60
80
100 ControlHyperthermia
** *
* Significantly lower than control (P<0.05)
Hyperthermia Reduces Voluntary Muscle Force Activation
Nybo & Nielson JAP 2001
Exercise to exhaustion (60%VO2max) in hot or temperate;sustained MVC knee, voluntary activation by electrical stimulation to nervus femoris
(Control Tc = 38oC; Hyperthermia Tc = 40oC)
Time (s)0 20 40 60 80 100 120 140
IEM
G in
% o
f max
0
40
60
80
100ControlHyperthermia
*
* significantly lower than control (P<0.05)
83%
54%
Muscle Metabolism & Heat Stress
• Muscle Blood Flow - Unchanged• Muscle Glycogen Utilization – Increased (not all)
• Fink et.al. EJAP 1975 • Febbraio JAP 1994• Jentjens JAP 2001
• Muscle Lactate Accumulation – Increased• Young et.al. JAP 1985• Febbraio JAP 1994
37.0 98.6
39.0
40.0
41.0
42.0
38.0
?
CV
Pathobiology
CNS & CV
Mec
hani
sm(s
)?
100.4
102.2
104.0
105.8
107.6C F
Summary: Heat Stress & Exercise Performance Reduction
modified from: Cheuvront & Sawka JKLES 2001
• Heat Stress Reduces Aerobic Performance • Core Temperature Tolerance is Climate & Population Specific• Multiple Mechanism Involvement • CV Strain Important• Role of CNS Shutdown?
Heat Acclimation
Actions of Heat Acclimation
• Thermal Comfort - Improved • Physiological Strain – Reduced• Exercise Performance - Improved
– Submaximal - Improved– Maximal - Same
Heat Acclimation Reduces Physiologic Strain
Days of Heat Exposure
0 2 4 6 8 10
Rec
tal T
empe
ratu
re, º
C
37
38
39
40
Hea
rt R
ate
100
120
140
160
180
Lind and Bass, Fed. Proc. 22: 704, 1963
Heat Acclimation Does Not Alter Core Temperature at Exhaustion
(60% VO2max, 40OC, 10% rh; VO2max = 49-74 ml/kg/min)
0 20 40 60
Time (min)
1 2 3 4 5 6 7 8 910
37.0
38.0
39.0
40.0
41.0
Esop
hage
al T
empe
ratu
re (°
C)
mean Tes = 39.7oCmean Tsk = 38.1oC
Nielson et.al. J. Physiol. (London) 1993
Heat Acclimation is Induced by:
• Repeated Heat Exposure Over Many Days • Heat Stress Sufficient to Increase Body
Temperature & Profuse Sweating• Duration - 100 min / day• Exposure - 4 to 14 days• Specific to Heat Stress
– Exercise / Rest– Intensity / Duration– Desert / Tropic
Time, h
0 1 2 3 4
Hea
rt R
ate,
b/m
in
80
100
120
140
160
180
Time, h
0 1 2 3 4
Rec
tal T
empe
ratu
re, º
C
36
37
38
39
40
Pre-Training11 wk Training; 4 d/wk8 Day HA
Aerobic Training Induces Partial Heat Acclimation
Cohen & Gisolfi, Med Sci Sports 14: 46, 1982
Physiology of Heat Acclimation
Core Temperature – Reduced Tolerance - UnchangedSweating - Improved Earlier Onset Higher Rate Redistribution (Tropic) Hidromeiosis Resistance (Tropic)Skin Blood Flow - Improved Earlier Onset Higher Rate (Tropic)Metabolic Rate – Lowered Lactate – Lowered Muscle Glycogen – UC or Reduced
Cardiovascular Stability - Improved Heart Rate - Lowered Stroke Volume – Increased Cardiac Reserve - Increased Blood Pressure - Better Defended Myocardial Compliance – Increased Myocardial Efficiency - ImprovedFluid Balance- Improved Thirst- Improved Electrolyte Loss - Reduced Total Body Water - Increased Plasma Volume - Increased & Better Defended
Thermal Comfort - Improved Exercise Performance - Improved
modified from Sawka et.al. Exercise & Sport Science 2000
Rectal Temperature (°C)
37.0 37.5 38.0 38.5 39.0
Sw
eatin
g R
ate,
ml/m
in
0
5
10
15
20
Day 1
Day 5
Day 9
Ladell Trans. Roy. Soc. Trop. Med. Hyg. 51: 189, 1957
38°C, 80% rh
Acclimation Improves Sweating ResponseDesert Climate
Tes oC37.0 37.5 38.0
Load
Sw
eat R
ate
mg/
(min
·cm
2 )
0.0
0.2
0.4
0.6
0.8Post-Heat
Post-Ex
Pre-Ex
Nadel et.al. JAP 1974
Acclimation Improves Sweating Responses More than Aerobic Training
(65% V02ma : 24o C )Lo
cal S
wea
t Rat
e
Acclimation
Training
Training
Tes oC37.0 37.5 38.0 38.5
Fore
arm
Blo
odflo
wcc
/(100
cc·m
in)
0
2
4
6
8
10
12
14
Post-Heat
Post-ExPre-Ex
Acclimation Improves Skin Blood Flow Response More than Aerobic Training
(75% V02max, 35oC, 75% RH )
Roberts et.al. JAP 1977
Acclimation
TrainingTraining
CA
RD
IAC
OU
TPU
T(1
min-1 )
11
12
13
14
Before AcclimatizationAfter Acclimatization
STR
OK
EVO
LUM
E(m
l)
60
80
100
TIME (min)0 10 20 30 40 50 60 70 80
HEA
RT
RA
TE(b
eats
min
-1)
130
150
170
190
210 Tr = 40oCTs = 39oC
Tr = 37.8oCT s= 37.5oC
Heat Acclimation Reduces Circulatory Strain(14 d;48oC)
Rowell et.al. JAP 1967
Better Maintained
Increased
Reduced
Day Of Heat Acclimation0 1 2 3 4 5 6 7 8 9
Sub
ject
s W
ith S
ynco
pe
0
5
10
15
20
Heat Acclimation Reduces Heat Syncope
Bean & Eichna, Fed. Proc. 1943
( n = 45)
( n = 38)
Days0 2 4 6 8 10
-8
-4
0
4
8
12
16
20
24
28
32
36
40
44
% Δ
Pla
sma
Volu
me
Days0 2 4 6 8 10
0
4
8
12
16
20
24
28
32
36
40 ABCDMEANVALUES
P < .05
Heat Acclimation & Plasma Volume Expansion(Hot/Wet; 40-50% VO2max)
% Δ
TC
P Ex
pans
ion
Senay et.al., JAP 1976
MeanMean
60
50
40
30
20
10
0.2 0.6 1.0 1.4 1.8 2.2
Alan & Wison, JAP 1971
Sweat Rate (mg / cm2 / min)
Swea
t Sod
ium
(meq
/ L)
UnacclimatedAcclimated
Heat Acclimation & Sweat Rate Effects on Sodium Loss
Met
abol
ic R
ate
(ml·k
g-1·m
in-1
)
0
15
16
17
18
19
50 min 110 min
Pre HAPost HA
49°C, 20% rh, 1.56 m/sec
Acclimation Lowers Metabolic Rate during Exercise
Sawka et al. ASEM , 1983
Summary: Heat Acclimation & Acquired Thermal Tolerance
• Acclimation Reduces Strain & Improves Performance• Acclimation is Specific to Type of Heat Strain• Improved Evaporative Cooling is Critical to Acclimation• Cardiovascular, Fluid, Metabolic Adaptations Support Acclimation•
Hydration / Blood Volume
0
10
20
30
40
50
60
32 38 43 49
90 100 110 120
oCoF
97
81
65
49
32
16
Km Miles
Dehydration Reduces Self-Paced Work
Adolph & Associates, Man in Desert, 1945
0
0L
10LFluid
Available
Montain et al. IJSM, 1998
(30ºC, 50% rh)
0 20 4036
37
38
39
0 20 400 20 40
n=9n=9 n=8
65% VO2max45% VO2max25% VO2max
EU3% BWL5% BWL
Cor
e Te
mp.
(ºC
)
Exercise Time (min)
Dehydration Increases Core Temperature
47% VO2max; 49ºC, 20% rh.
Dehydration Reduces Core Temperature Tolerance
Sawka et al. JAP. 1992
Eu 5% BWL
Cor
e Te
mp.
Tol
eran
ce (º
C)
38
40
39
*
0.2
0.6
1.0
1.4
Sw
eatin
g R
ate
(mg
/cm
/min
)
Core Temp. Core Temp.FB
F (m
l /10
0ml /
min
)36 37 38 39
Eu-
5% BWL
Dehydration Reduces Sweating & Skin Blood Flow During Exercise-Heat Stress
Sawka etal. AJP 1989 Kenney etal. JAP 1990
36 37 38 3
9
4
8
12
16
20
Eu-
5% BWL
7% BWL
37.0 38.0 39.0
20
30
40
50
0
0
0
0 Eu 3% BWL5% BWL
Who
le B
ody
Swea
ting
(g /
m2 / h
)
Rectal Temp. (ºC)
Sawka et al. JAP 1985
(25% VO2 max; 49 ºC, 20% rh)
Montain et al. JAP 1995
37 38 39
Eu 3% BWL
5% BWL
Loca
l Sw
eatin
g(m
g / c
m2 /m
in)
Esophageal Temp. (ºC)
(45% VO2 max;30ºC, 50% rh)
0.4
0.8
1.2
0.0
Dehydration Reduces Sweating Graded to Water Deficit
Car
diac
out
put
(L/m
in)
19
20
21
22
23
Time (min)0 20 40 60 80 100 120 140
Leg
Blo
od F
low
(L/m
in)
13
14
15
16
Heat & Dehydration Can Reduce Muscle Blood Flow(35°C, 45% rh; 61% VO2 max; 4%BWL)
-Gonzalez-Alonzo, et al, J. Physiol (London) 1998
Dehydration
Control
Does Hyperhydration Improve Thermoregulation?
Study Temperature SweatCore Skin Rate
Blyth & Burt (1961) nc Moroff & Bass (1965) Greenleaf & Castle (1971) nc nc ncLatzka et.al. (1997) nc nc ncLatzka et.al. (1998) nc nc ncNielsen (1971) Nielsen (1974) Gisolfi & Copping (1974) ncNadel et al. (1980) nc Grucza et al. (1987) nc Candas et al. (1988) nc nc ncLyons et al. (1990) nc
Montner et al. (1996) nc nc
Minutes of Exercise0 30 60 90
% P
lasm
a Vo
lum
e
0
5
10
15
20
Cor
e Te
mpe
ratu
re (°
C)
36
37
38
39
Acute Plasma Volume Expansion& Exercise - Heat Exposure
(45% VO2 max, 45 °C, 20% rh)
= msw
= Performance Time
Sawka et al. EJAP 1983
NS
Albumin Inf.
Control
UnacclimatedEuhydrated
1.0
0.8
0.6
0.4
0.2
36 37 38
Core Temperature ( ºC )
Loca
l Sw
eatin
g (m
g / c
m2 /
min
)Ss #1, EX ITS = 34.5
Erythrocyte Volume Expansion & Control of Sweating(45% VO2max ; 35º C 45% rh)
Sawka et al. JAP 1987
Pre-Infusion
Post-Infusion
Summary: Hydration / Blood Volume
• Dehydration Increases Thermal & Cardiovascular Strain• Dehydration Reduces Physical Work Performance• Plasma Hyperosmolality & Plasma Hypovolemia Contribute• Hyperhydration & Plasma Volume Expansion Do Not Improve Thermoregulation or Performance• Erythrocyte Volume Expansion Improves Thermoregulation & Performance