The Effect of Exercise Induced Muscle Damage
and Inflammation on Subsequent Thermoregulation
During Exercise in the Heat
Ryan Hillier-Smith, Cardiff University
Introduction
• Athletes and military personnel who perform arduous physical activity in high ambient
temperatures rely heavily on their thermoregulatory system to remove the heat which is
produced by exercising muscles (1)
• Any physiological or pathological process which can influence their ability to thermoregulate
may place them in a compromised condition when they begin to exercise in the heat
• This could predispose them to developing a potentially fatal exertional heat stroke (EHS) (2)
• An increase in the concentration of cytokines in the blood has been implicated in the aetiology
of EHS (3, 4)
• Pyrogenic cytokines, such as inter leukin-6 (IL-6), can raise the thermoregulatory set point
resulting in increased heat storage (5,6)
• Eccentric exercise, such as downhill running, causes exercise induced muscle damage (EIMD)
(7)
• This, in turn, results in an inflammatory response which includes an increase in the level of
circulating pyrogenic cytokines (8)
• This study investigated how EIMD and the associated inflammatory response affects the
ability of individuals to thermoregulate during subsequent bouts of exercise in high ambient
temperatures
Fig. 2; A participant performing the downhill exercise treatment
Methods
Results
• Repeated measures were performed on 3 male, recreationally active, sport science students
who completed 3 trials in a randomised order ((mean ± standard deviation) age 21 ± 1.2 yrs, BMI
21.8 ± 2.3 kg.m-2 and VO2max 63.3 ± 8.0 ml.kg-1.min-1)
• DOMS was significantly higher (p < 0.05) post-treatment in the downhill trial when compared to
the other trials
• The downhill trial involved 1 hour of 65% VO2max treadmill running at a 10% gradient decline
and was designed to represent EIMD
• The flat trial involved 1 hour of 65% VO2max treadmill running at a 1% gradient incline which
was designed as the control trial for EIMD
•The carbohydrate trial was the same as the flat trial but the participant was given a bolus of
carbohydrate which aimed to control for inflammation (9)
• Plasma [IL-6] was significantly higher (p < 0.05) during the downhill trial after the first heat
stress.
• Tc was significantly higher (p < 0.05) in the downhill trial after 40 minutes of heat stress 1
(Fig. 3;A)
• There was no significant difference in Tc between the trials during heat stress 2 (Fig. 3;B)
39.5
• These consisted of 40 minutes of 65% VO2max treadmill running at a 1% gradient incline in an
environmental chamber programmed to an ambient temperature of 33°C
39.0
Tc ( C)
• In all trials the exercise treatment was followed by 2 exercise heat stresses
• Heat stress 1 occurred 30 minutes post exercise treatment
•Heat stress 2 occurred 24.5 hours post exercise treatment (Fig. 1)
Day Two
Day One
37.5
Day One
Flat
Downhill
Carbohydrate
B
Tc ( C)
39.0
Trial Three
Day Two
38.0
39.5
• Core temperature (Tc) was measured using a rectal thermistor and represented exercising
thermoregulation
Day One
38.5
36.5
• Inflammation was measured using venous plasma IL-6 concentrations ([IL-6])
Trial Two
A
37.0
• Muscle damage was inferred from participant ratings of delayed onset muscle soreness
(DOMS) using Visual Analogue and 7 Point Likert Scales
Trial One
*
Day Two
38.5
38.0
37.5
37.0
36.5
1 Hour
14 Days
1 Hour
14 Days
1 Hour
Downhill
Run
Flat
Run
Run with
Carb
Ingestion
30
Minutes
30
Minutes
30
Minutes
Rest
Rest
Rest
40
Minutes
Heat
Stress 1
40
Minutes
Heat
Stress 2
40
Minutes
Heat
Stress 1
40
Minutes
Heat
Stress 2
40
Minutes
Heat
Stress 1
0
10
20
30
40
Time (minutes)
Fig. 3; Tc during heat stress 1 (A) and heat stress 2 (B). *P < 0.05 indicates a significant
difference between the downhill and carbohydrate trial. Values are means and standard
deviation for 3 participants
Conclusion
40
Minutes
Heat
Stress 2
Fig. 1; This schematic represents an example trial sequence for one participant
• This study suggests that EIMD and the accompanying inflammation causes an impairment in an
individual’s ability to thermoregulate when they undergo exercise heat stress shortly after the
muscle damaging event
• However, the results also suggest that this impairment of thermoregulation is not present 24.5
hours post the muscle damaging event
• Therefore, these findings have implications for athletes and military personnel who perform
muscle damaging exercises shortly before performing arduous physical activity in high ambient
temperatures
References
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