Male and Female Runners Underestimate Sweat Losses during 1 h Summer Run

To determine how accurately runners estimate their sweat losses. Twenty heat-acclimated female (age = 41 + or - 9 y, VO2max = 52 + or - 8 ml/kg/min, body fat = 23 + or - 4%) and 19 male (41 + or - 12 y, VO2max = 61 + or - 9 ml/kg/min, body fat = 14 + or - 5%) runners from the southeastern US completed a challenging outdoor road run between August and early September (WBGT = 24.1 + or - 1.5 [degrees]C) that allowed a finishing time of approximately 1 h. Runs began at approximately 06:45 or 18:45. Total sweat losses and losses by percent body were significantly greater (p < 0.01) for men (1797 + or - 449 mL, 2.3 + or - 0.6%) than women (1155 + or - 258 mL, 1.9 + or - 0.4%), but post-run sweat loss estimation accuracy did not differ between males (underestimation = 46.9 + or - 27.3%; 95% CI = 33.8-60.0%) and females (underestimation = 52.1 + or - 18.4%; CI = 43.5-60.7%).