Sweat rate and prediction validation during high-altitude treks on Mount Kilimanjaro

This study measured sweat rates (m(sw)) during high-altitude summer treks on Mt. Kilimanjaro to evaluate the efficacy of a recently developed fuzzy piecewise sweat prediction equation (Pw,sol) for application to high-altitude conditions. We hypothesized that the Pw,sol equation, adjusted for the barometric pressure (Pb) decreasing steadily at high altitude (Pw,sol+Alt), would allow for a more accurate prediction of m(sw) than Pw,sol unadjusted for altitude (Pw,sol(SL)). Fifteen men (43 ± 16 yr; 80 ± 22 kg) and seven women (46 ± 16 yr; 77 ± 18 kg) wearing hiking clothes (clo ∼1.15; clothing evaporative potential = 0.27) and carrying light loads (9 ± 2 kg), were studied during morning and afternoon treks (∼2-3 h) while ascending from 2,829 m to 3,505 m. After each trek, m(sw) was measured with specific biophysical parameters at 15-min intervals. During the trek day, Pb progressively declined (530 to 504 Torr), as solar radiation and ambient temperature (°C) rose transiently. During all treks, m(sw) ranged from 68 to 393 g·m(-2)·h(-1) (0.14 to 0.79 l/h). For each subject, derived Pw,sol(SL) and Pw,sol+Alt model outputs accurately predicted the morning and afternoon average m(sw) within a root mean square error of 0.145 l/h. No differences were found between Pw,sol(SL) and Pw,sol+Alt values. In conclusion, we report the first m(sw) measured during outdoor high-altitude activities and determined that Pw,sol(SL) equation can be used to predict fluid needs during high-altitude activities without alterations for lower Pb. This model prediction provides a valid water planning tool for outdoor activities at high altitude up to 3,500 m.