Sweat Electrolyte and Mineral Responses during 7 h of Exercise-Heat Stress

Abstract

Uncertainty exists regarding sweat mineral concentrations and effect of sustained sweating on sweat electrolyte and mineral composition. PURPOSE: Determine the effect of multiple hours of exercise-heat stress on sweat electrolyte and mineral concentrations. METHODS: Seven heat acclimated subjects (6 males, 1 female) completed 5 × 60 min of treadmill exercise (1.56 m/s, 2% grade) in a warm room (27°C, 40% rh, 1 m/s) with 20 min rest between each exercise period. Sweat was collected from a sweat collection pouch (Brisson et al., Eur J Appl Physiol 63: 269, 1991) attached to the upper back during exercise bouts 1, 3 and 5. Electrolytes and mineral elements were determined by using inductively coupled plasma emission spectrography (PerkinElmer model 3300; Norwalk, CT). RESULTS: Sweat sodium (863 ± 563 ug/ml), potassium (222 ± 48 ug/ml), calcium (16 ± 7 ug/ml), magnesium (1265 ± 566 ng/ml), copper (80 ± 56 ng/ml), and iron (47 ± 38 ng/ml) remained similar to baseline over 7 h of exercise-heat stress, whereas sweat zinc declined 42-45% after the initial hour of exercise-heat stress (Ex1 = 655 ± 360, Ex3 = 381 ± 167, Ex5 = 361 ± 283 ng/ml, P < 0.05). CONCLUSIONS: Sweat electrolyte losses during multiple hours of sustained sweating, as well as several minerals, can be predicted from initial sweat composition. Estimates of sweat zinc losses, however, will be overestimated if sweat zinc conservation is not accounted for in sweat zinc loss estimates. [Funded in part by PRMRP grant PR033015].