Football Practices in Hot Environments Impact Subsequent Days' Hydration

Abstract Ashley, CD, Lopez, RM, and Tritsch, AJ. Football practices in hot environments impact subsequent days' hydration. J Strength Cond Res 38(1): 90–96, 2024—The impact of proper hydration to prevent exertional heat illness in American football has not been evaluated during high school preseason football practices in a hot environment (wet-bulb globe temperature = 31.3 ± 1.8° C). The purposes of this study were to examine the accuracy of urinary hydration measures to assess body mass (BM) changes and to examine carryover effects of consecutive practices by comparing postpractice with the next prepractice values. Before and after each of 7 outdoor practices, 31 male high school football players (age = 16 ± 1 years, height = 181.2 ± 12.0 cm, BM = 85.7 ± 19.1 kg, body mass index = 20.8 ± 1.8) provided a urine sample and were weighed to assess hydration. Sensitivity and specificity of urine color (Ucol) and urine-specific gravity (USG) to determine BM changes were determined using receiver operating characteristic (ROC) analysis. Paired samples t-tests assessed carryover effects between practices. Repeated-measures analysis of variance assessed carryover effects across practices. Significance was set at p < 0.05. Sensitivity and specificity for using Ucol or USG to determine BM changes was not significant. For Ucol, there was a carryover effect from practice numbers 2 to 3, 6 to 7 am, 7 am to 7 pm (p < 0.001 for all), and 10 to 11 (p = 0.004); most with less than 24 hours between practices. The %BM loss (%BML) was significantly greater (p = 0.001 to 0.024) after 2-a-day practices. Effects of previous days' exercise in the heat, as evidenced by higher Ucol and %BL, are greater after 2-a-day practices, which occurred on later practice days. Athletes must replenish fluids during and between practices to remain euhydrated.