Predictors of sweat loss in man during prolonged exercise

Summary Nineteen healthy male subjects, differing in training status and\(\dot V_{{\text{O}}_{{\text{2max}}} } \) (52±1 ml · min⁻¹ · kg⁻¹, mean ±SEM; 43–64 ml · min⁻¹ · kg⁻¹, range), exercised for 1 h at an absolute workload of 192±8 W (140–265 W); this was equivalent to 70±1%\(\dot V_{{\text{O}}_{{\text{2max}}} } \) (66–74%). Each exercise test was performed on an electrically braked cycle ergometer at a constant ambient temperature (22.5±0.0° C) and relative humidity (85±0%). Nude body weight was recorded prior to and after each exercise test. Absolute sweat loss (body weight loss corrected for respiratory weight loss) during each test was 910±82 g (426–1665 g); this was equivalent to 1.3±0.1% (0.7–2.2%) of pre-exercise body weight (relative sweat loss). Weighted mean skin temperature and rectal temperature increased after 5 min of exercise from 30.5±0.3° C and 37.2±0.1° C respectively to 32.5±0.2° C and 38.8±0.1° C respectively, recorded immediately prior to the end of exercise. Bivariate linear regression and Pearson's correlation demonstrated absolute sweat loss was related to\(\dot V_{{\text{O}}_{{\text{2max}}} } \) (r=0.72,p<0.001), absolute exercise workload (r=0.66,p<0.01), body surface area (r=0.62,p<0.01), weight (r=0.60,p<0.01) and height (r=0.53,p<0.05). Relative sweat loss was related to\(\dot V_{{\text{O}}_{{\text{2max}}} } \) (r=0.77,p<0.001) and absolute exercise workload (r=0.59,p<0.01). There was no relationship between sweat loss (absolute or relative) and heart rate, skin temperature or rectal temperature. In addition, there was no relationship between rectal temperature or absolute exercise workload or\(\dot V_{{\text{O}}_{{\text{2max}}} } \). Stepwise multiple linear regression indicated\(\dot V_{{\text{O}}_{{\text{2max}}} } \) to be the most important predictor of absolute (r=0.72,F=18.27,p<0.001) and relative (r=0.77,F=24.58,p<0.001) sweat loss in man during prolonged exercise.