Peripheral Sweat Gland Function Improves With Humid Heat Acclimation

Background This study was conducted to determine if humid heat acclimation improves thermoregulatory function at the level of eccrine sweat gland. Methods Thirteen male volunteers participated in this study, which consisted of 2 h of exercise in a thermal environment of 35 degrees C and 75 relative humidity for 8 consecutive days. All trials were randomized and consisted of four 25-min exercise intervals with 5 min of seated rest. The four exercise intervals consisted of two bouts of treadmill walking 3 mph, 3 grade and two bouts of cycle ergometry power output of 60 W. Heart rate and core temperature were measured each minute during the trials and whole-body sweat rate was calculated for the duration of the exposure. On days 1, 4, and 8 peripheral sweat production was induced via pilocarpine iontophoresis on the flexor surface of both forearms. Results Mean rectal temperature and heart rate were significantly reduced by 0.5 degrees C and 17 bpm, respectively, and whole body sweat rate significantly increased by 20 during the 8-day heat acclimation protocol. Humid heat acclimation produced a significant 63 increase in pilocarpine-induced sweat rate. Conclusion The results strongly suggest that heat acclimation improves sweat gland function via a peripheral mechanism.