Determination of the Optimum Muscle Temperature for Maintaining Work Performance with Attenuation of Heat Stress in Human

The purpose of this study was to investigate the optimum muscle temperature required to maintain work performance with attenuation of heat stress. Nine male subjects (23±0.36 year) performed eight 8-sec bouts of maximal cycling exercise at a load intensity of 60% of their peak power output, with a 40-sec resting period between bouts, in a room maintained at 24.8±0.2°C and 52±1% relative humidity. The subjects worn trousers lined with tubes perfused water at 6°C, 17°C, 30°C or 44°C, and the target thigh muscle temperatures were 32°C (32.4±0.2°C), 34°C (34.4±0.2°C), 36°C (36.3±0.1°C) and 38°C (37.5±0.2°C), respectively. The peak power output from first to fourth bouts and the total work output during eight bouts were significantly greater at the 36°C and 38°C conditions than at the 32°C and 34°C conditions (p<;0.01), while there were no remarkable differences between the 36°C and 38°C conditions. After 10 minutes of the eight bouts of exercise, the tympanic temperature (Tty) was significantly elevated at the 38°C condition, but fell at the 32°C and 34°C conditions compared to that at baseline (p <; 0.01), while the Tty remained constant at the 36°C condition. The heart rate and rating of perceived exertion during eight bouts and the total sweat loss from the start to the end of experiment were significantly greater for the 38°C condition than for the 32°C and 34°C conditions. These results suggest that thigh temperature of approximately 36°C may be optimal to maintain repeated maximal cycling exercise performance with the attenuation of heat stress.