Abstract
BackgroundEndurance exercise capacity diminishes under hot environmental conditions. Time to exhaustion can be increased by lowering body temperature prior to exercise (pre-cooling). This systematic literature review synthesizes the current findings of the effects of pre-cooling on endurance exercise performance, providing guidance for clinical practice and further research.MethodsThe MEDLINE, EMBASE, CINAHL, Web of Science and SPORTDiscus databases were searched in May 2012 for studies evaluating the effectiveness of pre-cooling to enhance endurance exercise performance in hot environmental conditions (≥ 28°C). Studies involving participants with increased susceptibility to heat strain, cooling during or between bouts of exercise, and protocols where aerobic endurance was not the principle performance outcome were excluded. Potential publications were assessed by two independent reviewers for inclusion and quality. Means and standard deviations of exercise performance variables were extracted or sought from original authors to enable effect size calculations.ResultsIn all, 13 studies were identified. The majority of studies contained low participant numbers and/or absence of sample size calculations. Six studies used cold water immersion, four crushed ice ingestion and three cooling garments. The remaining study utilized mixed methods. Large heterogeneity in methodological design and exercise protocols was identified. Effect size calculations indicated moderate evidence that cold water immersion effectively improved endurance performance, and limited evidence that ice slurry ingestion improved performance. Cooling garments were ineffective. Most studies failed to document or report adverse events. Low participant numbers in each study limited the statistical power of certain reported trends and lack of blinding could potentially have introduced either participant or researcher bias in some studies.ConclusionsCurrent evidence indicates cold water immersion may be the most effective method of pre-cooling to improve endurance performance in hot conditions, although practicality must be considered. Ice slurry ingestion appears to be the most promising practical alternative. Interestingly, cooling garments appear of limited efficacy, despite their frequent use. Mechanisms behind effective pre-cooling remain uncertain, and optimal protocols have yet to be established. Future research should focus on standardizing exercise performance protocols, recruiting larger participant numbers to enable direct comparisons of effectiveness and practicality for each method, and ensuring potential adverse events are evaluated.
Highlights
Endurance exercise capacity diminishes under hot environmental conditions
A recent review evaluated the data of six International Association of Athletics Federations (IAAF) Gold Labeled Road Marathon races from 2001 to 2010 to determine which environmental factors have the largest impact on race performance [4]
Not all endurance events follow a linear model of performance decline with increasing environmental temperature [5], it is apparent that hot environmental temperatures above an optimum impair endurance exercise performance
Summary
Endurance exercise capacity diminishes under hot environmental conditions. Time to exhaustion can be increased by lowering body temperature prior to exercise (pre-cooling). This systematic literature review synthesizes the current findings of the effects of pre-cooling on endurance exercise performance, providing guidance for clinical practice and further research. Endurance exercise capacity has been reported to be diminished when exercising in hot environmental conditions, compared with normal and cold conditions [1,2,3]. The authors reported a median optimum environmental temperature of 6.2°C for men and 6.8°C for women. A separate study reported that higher environmental temperatures reduce the time taken to reach volitional fatigue when cycling at a fixed intensity (70% maximal aerobic capacity (VO2max)). Not all endurance events follow a linear model of performance decline with increasing environmental temperature [5], it is apparent that hot environmental temperatures above an optimum impair endurance exercise performance
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