Possible biphasic sweating response during short-term heat acclimation protocol for tropical natives

Abstract

The aim of the present study was to evaluate the sweat loss response during short-term heat acclimation in tropical natives. Six healthy young male subjects, inhabitants of a tropical region, were heat acclimated by means of nine days of one-hour heat-exercise treatments (40±0°C and 32± 1% relative humidity; 50% V̇O2peak on a cycle ergometer). On days 1 to 9 of heat acclimation whole-body sweat loss was calculated by body weight variation corrected for body surface area On days 1 and 9 rectal temperature (Tre) and heart rate (HR) were measured continuously, and rating of perceived exertion (RPE) every 4 minutes. Heat acclimation was confirmed by reduoed HR (day 1 rest: 77±5 b·min-1; day 9 rest: 68±3 b·min-1; day 1 final exercise: 161±15 b·min-1; day 9 final exercise: 145±11 b·min-1, p<0.05), RPE (13 vs. 11, p<0.05) and T re (day 1 rest: 37.2±0.2°C; day 9 rest: 37.0±0.2°C; day 1 final exercise: 38.2±0.2°C; day 9 final exercise: 37.9±0.1°C, p<0.05). The main finding was that whole-body sweat loss increased in days 5 and 7 (9.49±1.84 and 9.56±1.86g·m-2·min-1, respectively) compared to day 1 (8.31±1.31g·m-2·min -1, p<0.05) and was not different in day 9 (8.48±1. 02g·m-2·min-1) compared to day 1 (p>0.05) of the protocol. These findings are consistent with the heat acclimation induced adaptations and suggest a biphasic sweat response (an increase in the sweat rate in the middle of the protocol followed by return to initial values by the end of it) during short-term heat acclimation in tropical natives.