title: 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.
authors.affiliation: Dept. of Health, Physical Education and Recreation, University of North Alabama, Florence, AL.
authors.forename: Eric K
authors.initials: EK
authors.lastname: O'Neal
authors.forename: Brett A
authors.initials: BA
authors.lastname: Davis
authors.forename: Lauren K
authors.initials: LK
authors.lastname: Thigpen
authors.forename: Christina R
authors.initials: CR
authors.lastname: Caufield
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Horton
authors.forename: Joyce R
authors.initials: JR
authors.lastname: McIntosh
mesh_terms: D001835:Body Weight; D006801:Humans; D012420:Running; D013542:Sweat; D013546:Sweating; D013696:Temperature