Hydration Indices, Sweat Variables, and an Educational Intervention of Youth Football Campers

Abstract

PURPOSE: The purpose of this study was to measure sweat rate (SR), fluid consumption (FC), hydration status, and forearm [sweat-electrolyte] during a football camp consisting of practices (PR) and games (GA). An educational intervention (EI) utilizing these data was also examined. METHODS: Thirty-five boys (9–15 y; mean ± SD: 12±2y, 156 ± 12 cm, 52.9 ± 13.6 kg, 4 ± 2 y football experience) volunteered as part of a 5-day summer football camp with 3 (∼2 h) practices per day (WBGT: 25.6 ± 0.5°C). Subjects (stratified for age and mass) were randomly assigned to a non-intervention (NI) or EI group. Group comparisons were analyzed for differences between young (Y= 9–12y, n=22) and old (O= 13–15, n=13). EI took place on days 1–4 and lasted ∼5 min. Sweat patches applied to the forearm were used to quantify sweat-electrolyte (Na+ and K+) concentrations. RESULTS: Independent of group or age, GA SR (1.30 ± 0.57 L/hr) was significantly greater than PR SR (0.65 ± 0.35 L/hr, p=0.002). GA FC (1.00 ± 0.63 L/hr) was not significantly different from PR FC (0.79 ± 0.63L/hr, p=0.13). SR and baseline body weight (BW) were positively correlated (r=0.63, p<0.001). Average SR (1.02 ± 0.34 L/hr) and FC (0.96 ± 0.31 L/hr) in O was significantly greater than Y (SR= 0.64 ±0.26 L/hr, FC= 0.69 ± 0.24 L/hr, p<0.01). Initial Usg (1.024 ± 0.004) and urine osmolality (920.0 ± 164.5 mOsm/L, Uosm) significantly decreased by day 4PM (p<0.05). There were no significant differences in forearm sweat Na+ or K+ over time, or between Y (Na=31.9 ± 3.4 mEq/L, K= 7.7 ± 0.7 mEq/L) and O (Na= 33.0 ± 3.7 mEq/L, K= 8.3 ±0.8 mEq/L, p>0.05). PM to next-day AM weight loss was significantly less in EI compared to NI (p=0.01). AM Usg and Uosm were significantly lower than PM values (p<0.05). Campers replenished ∼100% of SR fluid losses during PR but only 76% during GA. Uosm averaged over 795 mOsm/L for days 2–5. CONCLUSIONS: Youth football players sweat more during GA than PR and rehydrate better during PR than GA. This may be due to coach encouragement, break time availability, and exercise intensity. Football campers arrived to camp hypohydrated but improved somewhat by day 4. FC matched SR during activities, but did not offset hypohydration because rehydration outside of PR and GA was likely inadequate. Sponsored by Gatorade Sports Science Institute®.