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A-26 Free Communication/Poster - Heat Stress and Fluid Balance: Focus on Youth: MAY 28, 2008 7: 30 AM - 12: 30 PM: ROOM: Hall B

Voluntary Drinking, Body Hydration and Aerobic Performance of Adolescent Male Athletes Running in the Heat

1333

Board #72 May 28 9:30 AM - 11:00 AM

Wilk, Boguslaw FACSM; Timmons, Brian W.

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Medicine & Science in Sports & Exercise: May 2008 - Volume 40 - Issue 5 - p S187
doi: 10.1249/01.mss.0000322269.99038.f2
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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

©2008The American College of Sports Medicine