We have previously shown that beverage flavoring and carbohydrate (CHO) and NaCl stimulate voluntary fluid intake in non-athletic children cycling at a moderate intensity in the heat, thereby preventing dehydration.
PURPOSE: This study investigated the effect of beverage flavoring and composition on voluntary fluid intake, body hydration, and aerobic performance in heat-acclimated adolescent male athletes running in the heat at a higher intensity and with much shorter rest periods, than in our previous studies.
METHODS: Nine 12- to 15-year-old male cross-country runners (VO2max: 59.2±1.3 mL·kg−1·min−1) underwent at least 4 heat-acclimation sessions (80 min each), followed by three experimental sessions. All sessions were performed at 30°C, 60-65% relative humidity. Each experimental session comprised five 15-min treadmill runs at a speed eliciting 65% VO2max, interspersed by 5 min rest. Ten min after the last treadmill bout, an aerobic performance test (APT - running to exhaustion at a speed eliciting 90% VO2max) was completed. The experimental sessions were identical, except for the beverage that the subjects drank ad libitum: water (W), flavored water (FW), and FW with 6% CHO and 18 mmol·L−1 NaCl (CNa) assigned in a counterbalanced order. Drink intake and body weight (BW) were monitored periodically.
RESULTS: Voluntary fluid intake was slightly higher than sweat loss in CNa (1223±111 vs. 1098±91 g), but slightly lower in W (973±129 vs. 1106±89 g) and FW (1063±79 vs. 1113±88 g). 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 APT (−0.2±0.2 %BW in CNa, and −0.5±0.2 %BW in W and FW). The APT was statistically not different among experimental trials (W: 8.24±0.71 min, FW: 7.45±0.16 min, and CNa: 9.09±0.9 min).
CONCLUSION: In contrast to previous findings in non-athletic, unacclimatized boys cycling at a moderate intensity (50% VO2max), 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. This likely resulted in similar aerobic performance observed in the W, FW and CNa trials.
Supported by Gatorade Sports Science Institute