A comparison of human thermoregulatory response following dynamic exercise and warm-water immersion

Abstract

We tested the hypothesis that the prolonged elevated plateau of esophageal temperature (T _es) following moderate exercise is a function of some exercise-related factors and not the increase in heat content andT _es during exercise, by comparing the response to increaseT _es during exercise (endogenous heating) and warm-water immersion (exogenous heating). Nine healthy, young [24.0 (1.9) years] subjects performed two separate experiments: (1) 15 min of treadmill exercise at 70%$\dot VO_{2max}$ and 15 min rest in a climatic chamber at 29°C, followed by 15 min of immersion in a 42°C water bath and a further 60 min of recovery in the climatic chamber [exercise-water (EW)]; and (2) 15 min of immersion in a 42°C water bath followed by 60 min of recovery in the climatic chamber [water-only (WO)]. Esophageal (T _es) and skin (T _sk) temperatures were recorded at 5-s intervals throughout. TheT _ea at which the forearm to finger temperature gradient (T _fa-T _fi) abruptly decreases was used to identify the threshold for forearm cutaneous vessel dilation (Th_dil) during exercise. Pre-exerciseT _es values were 36.64°C and 36.74°C for EW and WO respectively. The EW post-exerciseT _ea value fell to a stable level of 37.12°C and this value differed by 0.48°C (P < 0.05) from baseline, but was similar to Th_dil (37.09°C). Despite a 1.2°C increase inT _es during the subsequent warm-water immersion,T _es returned to the post-exercise value (37.11°C). The WO post-immersionT _es fell to a stable plateau of 36.9°C, which was not statistically different from the pre-immersion T_es. The data for both warm-water treatments support the hypothesis that increases inT _es and heat content alone are not the primary mechanisms for the post-exercise elevation inT _es and Th_dil. These data also support our previous observation that the exercise-induced elevation in Th_dil persists into recovery.