Wilk, B., & Timmons, B. W. (2008). Voluntary drinking, body hydration and aerobic performance of adolescent male athletes running in the heat. ACSM 55th Annual Meeting Indianapolis, Presentation Number 1333.

This study investigated the effect of beverage flavoring and composition on voluntary fluid intake, body hydration, and aerobic performance in heat-acclimated adolescent male cross-country runners (N = 9) running in the heat. Ss underwent at least four heat-acclimation sessions (80 minutes each), followed by three experimental sessions. All sessions were performed at 30°C with 60-65% relative humidity. Experimental sessions comprised five 15-minute treadmill runs at a speed eliciting 65% VO2max, interspersed by five minutes of rest. Ten minutes after the last treadmill bout, an aerobic performance test was completed. Experimental sessions were identical, except for the beverage that Ss drank ad libitum: water, flavored water, and flavored water with 6% carbohydrate, and 18 mmol/l NaCl assigned in a counterbalanced order.

Voluntary fluid intake was slightly higher than sweat loss in NaCl group, but slightly lower in the water and flavored water groups. Although lower than total fluid losses through sweating, respiration, and urine output, voluntary fluid intake during intermittent running was sufficient to prevent major dehydration by the start of the aerobic performance test. There was no difference among the various fluid groups on the aerobic performance test.

Implication. Heat-acclimated adolescent runners voluntarily consumed enough fluid (irrespective of flavoring and content) to remain well hydrated while running at 65% VO2max in the heat.

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