Runners Greatly Underestimate Sweat Losses Before and After a 1-hr Summer Run

Abstract

The purpose of this study was to determine how accurately runners estimate their sweat losses. Male (n = 19) and female (n = 20) runners (41 ± 10 yr, VO2max 57 ± 9 ml · kg(-1) · min(-1) from the southeastern U.S. completed an ~1-hr run during late summer on a challenging outdoor road course (wet bulb globe temperature 24.1 ± 1.5 °C). Runs began at ~6:45 a.m. or p.m. Before and after running, participants filled race-aid-station paper cups with a volume of fluid they felt would be equivalent to their sweat losses. Total sweat losses and losses by percent body weight differed (p < .01) between men (1,797 ± 449 ml, 2.3% ± 0.6%) and women (1,155 ± 258 ml, 1.9% ± 0.4%). Postrun estimates (738 ± 470 ml) were lower (p < .001) than sweat losses (1,468 ± 484 ml), equaling underestimations of 50% ± 23%, with no differences in estimation accuracy by percentage between genders. Runners who reported measuring changes in pre- and postrun weight to assess sweat losses within the previous month (n = 9, -54% ± 18%) were no more accurate (p = .55) than runners who had not (n = 30, -48% ± 24%). These results suggest that inadequate fluid intake during runs or between runs may stem from underestimations of sweat losses and that runners who do assess sweat-loss changes may be making sweat-loss calculation errors or do not accurately translate changes in body weight to physical volumes of water.

Trapped sweat in basketball uniforms and the effect on sweat loss estimates

“…In this study (O'Neal et al. ), the percentage of sweat loss trapped in the runner's clothing was higher (26% for men and 22% for women) than that of Cheuvront et al. () or this study, perhaps due in part to the higher relative humidity (mean of 86 and 72% during morning and evening runs), which could have limited the rate of sweat evaporation.…”

“…; Noonan and Stachenfeld ; O'Neal et al. ) have shown that trapped sweat in clothing can lead to underestimations in sweat loss; however, this study is the first to measure trapped sweat in basketball uniforms and demonstrate that the magnitude of trapped sweat and the associated errors in sweat loss estimates are dependent upon common exercise/sport factors (exercise intensity, exercise duration, and sweat loss).…”

“…O'Neal et al. () reported that mean mass of sweat retained in shoes and clothing and toweled off skin after a ~1‐h outdoor run was 0.49 kg and 0.28 kg in men and women, respectively. In this study (O'Neal et al.…”

“…; O'Neal et al. ) and the ice hockey uniforms (Noonan and Stachenfeld ). For example, the interindividual range in the treadmill runners' trapped sweat was 0.03–0.66 kg (Cheuvront et al.…”

“…; Noonan and Stachenfeld ; O'Neal et al. ). Such data could be instrumental in the development of best practice recommendations for measuring sweat losses in the field (Cheuvront and Kenefick ).…”