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

This study examined whether muscle injury and the accompanying inflammatory responses alter thermoregulation during subsequent exercise-heat stress. S ixteen 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 bo dy (LBE) exercise. In experiment 1, eight subjects performed treadmill exer cise before and 6, 25, and 30 h after UBE and then 6, 25, and 30 h after LB E. 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 sig nificantly elevated creatine kinase levels (P < 0.05), but only LBE increas ed (P < 0.05) interleukin-6 levels. In experiment 1, core temperatures befo re and during exercise-heat stress were similar for control and after UBE, but some evidence for higher core temperatures was found after LBE. In expe riment 2, core temperatures during exercise-heat stress were 0.2-0.3 degree s C (P < 0.05) above control values at 2 and 7 h after LBE. The added therm al 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 > 0.0 5) to muscle soreness (r = 0.47 at 6-7 h), plasma interleukin-6 (r = 0.35 a t 6-7 h), or peak creatine kinase levels (r = 0.22). Local sweating respons es (threshold core temperature and slope) were not altered by UBE or LBE. T he results suggest that profuse muscle injury can increase body core temper ature during exercise-heat stress and that the added heat storage cannot be attributed solely to increased heat production.