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
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• Temperature Regulation During Exercise• Exercise Performance & Exhaustion• Heat Acclimation• Hydration / Blood Volume
Outline
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Temperature Regulation During Exercise
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Heat Stress & Physiological Temperature Regulation
Gisolfi & Wenger ESSR 1984
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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
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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)
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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
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Summary: Temperature Regulation
• Metabolic Rate Dictates Required Heat Loss • Warmer Environment Greater Need for Evaporation• Core Temperature Increase
• Exercise Intensity• Climate
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Exercise Performance & Exhaustion
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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
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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
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% 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)
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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
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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
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Heat Stress Increases Circulatory Strain by Skin Blood Flow / Volume
Rowell Human Circulation 1986
SKBFmax= 7.8 L/min
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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)
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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
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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%
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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
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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?
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Heat Acclimation
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Actions of Heat Acclimation
• Thermal Comfort - Improved • Physiological Strain – Reduced• Exercise Performance - Improved
– Submaximal - Improved– Maximal - Same
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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•
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Hydration / Blood Volume
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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
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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
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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
*
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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
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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
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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
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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
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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
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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
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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