Optimizing Cold Water Immersion For Exercise-Induced Hyperthermia

Abstract

PURPOSE: Overwhelming evidence indicates cold water immersion (CWI) provides superior cooling rates for hyperthermic individuals. This study aimed to evaluate the effect of CWI on the cooling rate in healthy adults subject to exercise-induced hyperthermia. METHODS: Eleven studies qualified for inclusion. Included in the meta-analysis were standardized mean difference (SMD; Hedges’ g) including 95% confidence intervals (CI), parallel with mean ± SD of cooling rates for CWI from each study/data set. Using a random-effects model, heterogeneity was established computing the I2 statistic. RESULTS: Thirteen cooling rates pertaining to 159 subjects show a significant overall SMD = 2.48 (95% CI: 1.57-3.39, P < 0.0001). CWI elicited 2.3-fold greater cooling rate than passive rest (CON): CWI 0.14 ± 0.07°C·min-1 vs. CON 0.06 ± 0.04°C·min-1. Meta-regression showed immersion time was not correlated to cooling rate (Cochran’s Q = 2.98, P = 0.08). Subgroup analyses revealed that immersion water temperature was a strong moderator of cooling rate, with the fastest cooling rate using <5°C (SMD = 8.29, P < 0.0001) and 5-10°C CWI (SMD = 2.18, P = 0.028). Using the mean cooling rate from this meta-analysis, it is projected that it requires ∼7, 10, 14, 23 min to cool a hyperthermic individual from 40.0°C to 38.6°C, for <5°C, 5-10°C, 10-15°C CWI, and CON, respectively. CONCLUSION: CWI should be encouraged for treating exercise-induced hyperthermia whenever possible, using as cold a water temperature as possible.