Transcript The Effect of Exercise Induced Muscle Damage

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
1. Wendt, D., van Loon, L.J.C., and van Marken Lichtenbelt, W.D. (2007). Thermoregulation during exercise in the heat: strategies for maintaining health and performance. Sports Medicine, 37, 669–682.
2. Walsh, N.P., Gleeson M., Pyne, D.B., Nieman, D.C., Dhabhar, F.S., Shephard, R.J., Oliver, S.J., Bermon, S. and Kajeniene, A. (2011). Position statement part two: Maintaining immune health. Exercise Immunology. Review, 17, 64–103
3. Shephard, R.J. and Shek, P.N. (1999). Immune dysfunction as a factor in heat illness. Critical Reviews in Immunology, 19, 285-302
4. Lim, C.L. and Mackinnon, L.T. (2006). The roles of exercise-induced immune system disturbances in the pathology of heat stroke: the dual pathway model of heat stroke. Sports Medicine, 36, 39-64
5. Bradford, C.D., Cotter, J.D., Thorburn, M.S., Walker, R.J. and Gerrard, D.F. (2007). Exercise can be pyrogenic in humans. The American Journal of Physiology - Regulatory Integrative and Comparative Physiology, 292, R143-149
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7. Fielding, R.A., Manfredi, T.J., Ding, W., Fiatarone, M.A., Evans, W.J. and Cannon, J.G. (1993). Acute phase response in exercise. III. Neutrophil and IL-1 beta accumulation in skeletal muscle. American Journal of Physiology - Regulatory
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8. Cannon, J.G. and Kluger, M.J. (1983). Endogenous pyrogen activity in human plasma after exercise. Science, 220, 617-619
9. Starkie, R.L., Arkinstall, M.J., Koukoulas, I., Hawley, J.A. and Febbraio, M.A. (2001). Carbohydrate Ingestion attenuates the increase in plasma interleukin-6, but not skeletal muscle interleukin-6 MRNA, during exercise in humans. The Journal
of Physiology, 533, 585-591