Heat Loss Responses at the Onset of Dynamic Exercise in Endurancetrained Men Under Mildly Heated Conditions

Abstract

2138 Heat loss responses at the onset of dynamic exercise are modulated by non-thermal factors. However, it remains unclear whether endurance training enhances these heat loss responses. PURPOSE: This study investigated the heat loss responses at the onset of dynamic exercise in endurance-trained men under mildly heated conditions. METHODS: Eight trained and nine untrained men (maximal oxygen uptake: VO2max 59.7 ± 1.7 vs. 42.7 ± 1.7 ml/kg/min, p<0.05) performed a cycle exercise in semi-supine position at 30, 50 and 70% VO2max for 60 s with at least 10 min interval in the mildly heated conditions. These bouts of exercises were conducted after each subject was exposed at Ta of 35°C and RH of 50%. RESULTS: The esophageal and mean skin temperatures showed almost steady in both the groups throughout the experiments. The heart rate, rating of perceived exertion, mean arterial pressure, and sweating rate (SR) from the non-glabrous skin (chest, forearm and thigh) increased linearly with a rise in exercise intensity in both groups. SR from the glabrous skin (palm) showed intensity-dependent responses only in the trained group. The mean SR of non-glabrous skin was significantly higher in the trained group than the untrained group (p<0.05). The slope of the regression line of mean SR-relative exercise intensity and mean SR-(oxygen uptake (VO2) were significantly steeper in the trained group than in the untrained group (p<0.05). Moreover, the mean CVC from the non-glabrous skin (chest and forearm) decreased markedly in the trained group compared with untrained groups at 50 and 70% VO2max (p<0.05). Both the slopes of regression lines relating CVC to relative exercise intensity and VO2 were significantly steeper in the trained group than the untrained group at both the non-glabrous and glabrous skins (p<0.05). CONCLUSIONS: Endurance training enhances SR and CVC responses without marked change in body temperatures at the onset of dynamic exercise. The training induces more increase in SR and decrease in CVC in both the sites of non-glabrous and glabrous skins.