Cheuvront, S. N., Woodard, M. R., Ruble, M. J., DeRuisseau, K. C., Ostler, D. M., & Haymes, E. M. (2000). Fluid intakes and thermoregulatory responses of female marathon runners in two environments. Medicine and Science in Sports and Exercise, 32(5), Supplement abstract 458.

Female marathon runners (N = 8) were studied during a 30-km treadmill run under two ambient conditions (WBGT 12+1 degrees and 25+1 degrees).

Sweat losses were significantly greater in the hot condition. Fluid intake replaced 64% (hot) and 76% (cool) of fluid loss, values that were not significantly different. Both fluid intake volumes kept dehydration at approximately 3% or less of body weight loss. Rectal temperatures at the end of the 30-km run were similar between conditions. Sweat loss was the single best predictor, although not a very good predictor, of final rectal temperature.

Women's ad lib fluid intakes during long runs were sufficient to maintain adequate thermoregulatory responses. Those intakes were at or below present fluid replacement guidelines.

Implication. Conscientious fluid intakes in long runs are sufficient to maintain adequate thermoregulatory conditions.

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