Impact of muscle injury and accompanying inflammatory response on thermoregulation during exercise in the heat

Abstract

This study examined whether muscle injury and the accompanying inflammatory responses alter thermoregulation during subsequent exercise-heat stress. Sixteen subjects performed 50 min of treadmill exercise (45-50% maximal O(2) consumption) in a hot room (40 degrees C, 20% relative humidity) before and at select times after eccentric upper body (UBE) and/or eccentric lower body (LBE) exercise. In experiment 1, eight subjects performed treadmill exercise before and 6, 25, and 30 h after UBE and then 6, 25, and 30 h after LBE. In experiment 2, eight subjects performed treadmill exercise before and 2, 7, and 26 h after LBE only. UBE and LBE produced marked soreness and significantly elevated creatine kinase levels (P < 0.05), but only LBE increased (P < 0.05) interleukin-6 levels. In experiment 1, core temperatures before and during exercise-heat stress were similar for control and after UBE, but some evidence for higher core temperatures was found after LBE. In experiment 2, core temperatures during exercise-heat stress were 0.2-0.3 degrees C (P < 0.05) above control values at 2 and 7 h after LBE. The added thermal strain after LBE (P < 0.05) was associated with higher metabolic rate (r = 0.70 and 0.68 at 2 and 6-7 h, respectively) but was not related (P > 0.05) to muscle soreness (r = 0.47 at 6-7 h), plasma interleukin-6 (r = 0.35 at 6-7 h), or peak creatine kinase levels (r = 0.22). Local sweating responses (threshold core temperature and slope) were not altered by UBE or LBE. The results suggest that profuse muscle injury can increase body core temperature during exercise-heat stress and that the added heat storage cannot be attributed solely to increased heat production.

Exercise-Induced Interleukin-6 and Metabolic Responses in Hot, Temperate, and Cold Conditions

“…The differences in oxygen and substrate utilization between trials indicate that factors other than exercise intensity may play a role in plasma IL-6 concentration. The findings from the current study agree with other studies that have shown a minor increase in plasma IL-6 concentrations with endurance exercise but no effect of temperature (Cosio-Lima, Desai, Schuler, Keck, & Scheeler, 2011;Lim et al, 2009;Montain, Latzka, & Sawka, 2000;Starkie et al, 2005). Although temperature did not influence plasma IL-6 levels, exercise elicited a significant increase in plasma IL-6.…”

Repeated muscle damage blunts the increase in heat strain during subsequent exercise heat stress

“…The final Tre on EIMD trial 2 was similar to the final Tre observed in the control group during HS on both CON trials (Fig 3b), although we acknowledge that these groups were composed of different individuals, so are not directly comparable. In our previous study (Fortes et al 2013), final Tre was 0.53 °C higher during HS following EIMD compared to control non-muscle damaging exercise in a repeated measures design, whilst Montain et al (2000), also demonstrated ~0.3 °C greater body temperature during HS following muscle damaging exercise compared to control exercise. It therefore appears that a prior bout of EIMD provides a significant degree of protection against the increased heat strain that EIMD elicits during subsequent exercise-heat-stress.…”

“…Non-heat-acclimated individuals undertaking heavy training bouts with an eccentric component in the heat are likely at increased risk of developing EHI (Fortes et al 2013;Montain et al 2000) e.g. athletes performing unaccustomed exercise, or soldiers running or walking across mountainous terrain.…”

“…walking downhill/jumping/lunging etc.). We (Fortes et al 2013), and others (Montain et al 2000), have shown that prior exercise-induced muscle-damage (EIMD) increases heat strain during exercise-heat-stress conducted shortly after muscle damage. For example, final rectal temperature (Tre) was 0.53°C higher during 40 min of moderate exercise-heat-stress conducted 30 min after 1-hour of EIMD, compared to identical exercise-heat-stress conducted 30 min after 1-hour of nonmuscle-damaging control exercise (Fortes et al 2013).…”

Exercise can be pyrogenic in humans

“…However, this effect has only been evidenced from higher exercising T core during exercise performed many hours after the damaging stimulus (6,34) and may depend on prior migration of activating agents such as neutrophils, macrophages, and PAF (41, 51). The exercise undertaken in this study was not performed to exhaustion, and none of the subjects reported difficulty or injury as a consequence of the exercise schedules.…”