Runners greatly underestimate sweat losses before and after a 1-hr summer run
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. © 2012 Human Kinetics, Inc.
International Journal of Sport Nutrition and Exercise Metabolism
O'Neal, E., Davis, B., Thigpen, L., Caufield, C., Horton, A., & McIntosh, J.
(2012). Runners greatly underestimate sweat losses before and after a 1-hr summer run. International Journal of Sport Nutrition and Exercise Metabolism, 22 (5), 353-362.