EFFECT OF SWEAT GLAND INACTIVATION ON SKIN TEMPERATURE AND SKIN BLOOD FLOW DURING EXERCISE IN THE HEAT

Abstract

Sweat evaporation is the primary means for heat dissipation during exercise. The purpose of this study was to investigate the effect of sweat gland inactivation on sweat gland recruitment, skin temperature and skin blood flow during exercise in the heat. Nine subjects used tap-water iontophoresis with an electrical current of 7–20 mA on a 65 cm2 area of the anterior mid-forearm. Subjects were treated for 7 hr over seven consecutive days, and treatment to the non-dominant and dominant forearm was randomly assigned. After completing the treatment, subjects exercised at a light intensity (70 W) for 30 min in a warm environment (32°C, 50% RH) to promote sweating. Skin temperature and skin blood flow were measured during exercise at 0, 15, and 30 min with a YSI skin surface probe and a TSI laser Doppler, respectively. Immediately after exercise, sweat gland recruitment was measured with iodine-impregnated paper. The iontophoresis treatment decreased the number of active sweat glands by 75% which significantly increased skin temperature and skin blood flow. Post-hoc analysis indicated that the treated arm at 30 min was 0.6 °C warmer (P = 0.027) and had a 0.7 mol·100 ml−1 ·min−1 higher skin blood flow (P = 0.021). The data suggest that tap-water iontophoresis was an effective means of reducing sweat gland recruitment during exercise in the heat. These results illustrate the importance of sweat evaporation on skin temperature on skin temperature and skin blood flow for heat dissipation during exercise.