Hydration and Human Athletic Performance: A Meta-Analysis
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It is claimed by the US Army and International Olympic Committee that dehydration, especially if greater than 2% body mass lost, impairs performance in exercise (Cheuvront, Carter, & Sawka, 2003; Convertino et al., 1996; Rodriguez, Di Marco, & Langley, 2009). Yet many runners and cyclists experience exercise-induced dehydration while maintaining excellent performance—and even setting record times. Using a meta-analysis, I tested the veracity of the claims that exercise-induced dehydration impairs exercise performance. The analysis compared euhydrated and dehydrated groups that performed either fixed-intensity (e.g., cycling or treadmill protocols maintained at constant speed until exhaustion) or variable-intensity exercise (e.g., running a marathon). A random effects meta-analysis was used to estimate the range of effect sizes associated with dehydration. Dehydration significantly diminished the performance of athletes during fixed-intensity exercises. In contrast, dehydration slightly improved the performance of athletes during variable-intensity exercises. Hydration thus had a significant effect on the performance of endurance athletes, but the effects of dehydration depend on the nature of the physical activity.