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

Gonzalez RR, Kenefick RW, Muza SR, Hamilton SW, Sawka MN. Sweat rate and prediction validation during high-altitude treks on Mount Kilimanjaro. J Appl Physiol 114: 436-443, 2013. First published December 27, 2012; doi: 10.1152/japplphysiol.01176.2012.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 ((P) over dotw,sol) for application to high-altitude conditions. We hypothesized that the (P) over dotw,sol equation, adjusted for the barometric pressure (P-B) decreasing steadily at high altitude ((P) over dotw,sol + Alt), would allow for a more accurate prediction of msw than (P) over dotw,sol unadjusted for altitude ((P) over dotw,sol(SL)). Fifteen men (43 +/- 16 yr; 80 +/- 22 kg) and seven women (46 +/- 16 yr; 77 +/- 18 kg) wearing hiking clothes (clo similar to 1.15; clothing evaporative potential = 0.27) and carrying light loads (9 +/- 2 kg), were studied during morning and afternoon treks (similar to 2-3 h) while ascending from 2,829 m to 3,505 m. After each trek, msw was measured with specific biophysical parameters at 15-min intervals. During the trek day, P-B progressively declined (530 to 504 Torr), as solar radiation and ambient temperature (degrees C) rose transiently. During all treks, msw ranged from 68 to 393 g.m(-2).h(-1) (0.14 to 0.79 l/h). For each subject, derived (P) over dotw,sol(SL) and (P) over dotw,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 (P) over dotw, sol(SL) and (P) over dotw,sol+Alt values. In conclusion, we report the first msw measured during outdoor high-altitude activities and determined that (P) over dotw,sol(SL) equation can be used to predict fluid needs during high-altitude activities without alterations for lower P-B. This model prediction provides a valid water planning tool for outdoor activities at high altitude up to 3,500 m.