Abstract
We determined whether beverage flavoring and composition would stimulate voluntary drink intake, prevent dehydration, and maintain exercise performance in heat-acclimated adolescent males running in the heat. Eight adolescent (age, 13.7± 1.1years) runners (peak oxygen uptake, 59.5± 4.0mL·kg-1·min-1) underwent at least four 80-min exercise heat-acclimation sessions before completing 3 experimental sessions. All sessions were performed at 30°C and 60%-65% relative humidity. Each experimental session consisted of five 15-min treadmill runs at a speed eliciting 65% peak oxygen uptake, with a 5min rest prior to each run. Ten minutes after the final run, a time to exhaustion test was performed at a speed eliciting 90% peak oxygen uptake. Counterbalanced experimental sessions were identical, except for fluid intake, which consisted of tap water (W), flavored water (FW), and FW with 6% carbohydrate and 18mmol·L-1 NaCl (CNa) consumed ad libitum. Fluid intake and body weight were monitored to calculate dehydration. Voluntary fluid intake was similar to fluid losses in W (1032± 130 vs. 1340± 246g), FW (1086± 86 vs. 1451± 253g), and CNa (1259± 119 vs. 1358± 234g). As a result, significant dehydration was avoided in all trials (-0.45%± 0.68% body weight in W,-0.66%± 0.50% body weight in FW, and-0.13%± 0.71% body weight in CNa). Core temperature increased by ~1°C during exercise, but was not different between trials. Time to exhaustion was not different between trials and averaged 8.8± 1.7min. Under exercise conditions more closely reflecting real-life situations, heat-acclimatized adolescent male runners can appropriately gauge fluid intake regardless of the type of beverage made available, resulting in consistency in exercise performance.
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