Effect of Intensive and Repetitive Heat Exposure on the Sudomotor Activity

The sweating response is modulated in two different ways depending on adaptation conditions. In this work, we examined sudomotor activities before and after intensive and repetitive heat exposure. Nine male volunteers were exposed to 30-min half-body immersion in hot water (42 ± 0.5°C) at the same time of day on alternate days for 3 weeks. All experiments were performed in an automated climate chamber. Tympanic (Tty) and skin (Ts) temperatures were measured. Mean body temperature (mTb) was calculated. Sudomotor activities, including sweat onset time, sweat rate and volume, activated sweat gland density (ASGD) and output (ASGO), were tested in four regions of the skin: chest, abdomen, upper back and thigh. Basal Tty and mTb were found to decrease by 0.15°C (P < 0.05) and 0.16°C (P < 0.05), respectively. As a typical data (upper back), sweat onset time increased by 33.6% (P < 0.05) after heat acclimation. After heat acclimation, sweat rate decreased by 14.7% (P < 0.05), sweat volume decreased by 15.5% (P < 0.05) and ASGO also decreased by 11.1% (P < 0.05). ASGD decreased by 4.1% after heat acclimation without statistical significance. The data suggest that intensive and repetitive heat exposure induces suppression of sudomotor activities within 3 weeks.