Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure.
Level 1 - systematic review of randomized trials
Meta-analysis of controlled laboratory studies evaluating exercise performance.
PubMed 22763119 · doi:10.1136/bjsports-2012-090958
What was done
A meta-analysis evaluated 15 laboratory-based studies (28 effect estimates, 122 total subjects) comparing the effect of exercise-induced dehydration on endurance performance. Exercise testing protocols were categorized into ecologically valid (EV; time-trial exercise) or non-ecologically valid (NEV; clamped-intensity exercise) designs. Outcomes were standardized as percentage changes in power output between euhydrated and dehydrated conditions using random-effects meta-regression and mixed-effects models.
What was found
Under time-trial (EV) exercise conditions, exercise-induced dehydration resulted in a non-significant change in endurance performance of 0.09 ± 2.60% (p = 0.9). Under clamped-intensity (NEV) exercise protocols, dehydration reduced endurance performance by 1.91 ± 1.53% (p < 0.05). Body weight loss of 2% or greater significantly impaired performance only in NEV protocols (p = 0.03), not in EV time trials.
Why it matters
The widely cited rule that losing at least 2% of body weight to dehydration impairs endurance performance appears to be an artifact of fixed-intensity laboratory testing. Real-world, self-paced time-trial performance is preserved despite dehydration up to approximately 4% of body weight.
Limits
The total pooled sample was small (122 subjects across 15 studies). The abstract does not provide details on participant training status, sex distribution, heat stress conditions, or specific rehydration protocols across the primary studies.