Drink Composition, Voluntary Drinking And Aerobic Performance In Heat-acclimated Adolescent Male Athletes

Abstract

PURPOSE Previous research suggests that children who are non-athletes and not heat acclimated increase their voluntary drinking volume during intermittent lowintensity exercise, when the beverage is flavored and includes carbohydrate and NaCl (Wilk & Bar-Or, J. Appl. Physiol., 1996). This study was intended to assess the effect of beverage flavoring and composition on voluntary drinking pattern, body hydration and aerobic performance in the heat among adolescent male athletes who are partially heat acclimated and who exercise at a moderate-to-high intensity. METHODS Six 12- to 15-year-old endurance athletes, underwent chamber-based 4 to 6 heat-acclimation sessions, followed by 3 experimental sessions. The latter were held at 30 °C, 60% relative humidity and comprised five 15-min cycling bouts at 65% VO2max, interspersed by 5 min rest. This was followed by an aerobic performance test (APT - cycling to exhaustion at 90% VO2max). The three sessions were identical, except for the beverage that the subjects drank ad libitum: water (W), flavored water (FW), and FW with carbohydrate (6%) and NaCl 18 mmol.L−1 (CNa). These were assigned in counterbalanced order. Total time sustained during the APT was recorded and total mechanical work calculated. Drink intake, body weight (BW), physiologic and perceptual variables were monitored periodically. RESULTS Total sweat loss (from 841±87 g in W to 976±94 g in FW) and drink intake (from 843±242 g in CNa to 944±205 g in W) were similar in the three sessions. They were higher in our subjects than in non-acclimated boys exercising intermittently at 50% VO2max. Drinking was insufficient to prevent voluntary dehydration at the start of the APT (from −0.18 %BW in W to −0.69 %BW in FW). There were no inter-session differences in aerobic performance (total work from 56.4±10.5 kJoule in FW to 71.7±20.6 kJoule in W). CONCLUSION Irrespective of beverage flavoring and content, voluntary drinking volume during 110 min intermittent exercise (65% VO2max) in the heat is insufficient to prevent mild dehydration in partially heat-acclimated adolescent athletes. Nor does fluid flavoring and content affect maximal aerobic performance… Supported by Gatorade Sports Science Institute