Precooling and percooling (cooling during exercise) both improve performance in the heat: a meta-analytical review

Background Exercise increases core body temperature (Tc), which is necessary to optimise physiological processes. However, excessive increase in Tc may impair performance and places participants at risk for the development of heat-related illnesses. Cooling is an effective strategy to attenuate the increase in Tc. This meta-analysis compares the effects of cooling before (precooling) and during exercise (percooling) on performance and physiological outcomes. Methods A computerised literature search, citation tracking and hand search were performed up to May 2013. 28 studies met the inclusion criteria, which were trials that examined the effects of cooling strategies on exercise performance in men, while exercise was performed in the heat (>30 degrees C). 20 studies used precooling, while 8 studies used percooling. Results The overall effect of precooling and percooling interventions on exercise performance was +6.7 +/- 0.9% (effect size (ES)=0.43). We found a comparable effect (p=0.82) of precooling (+5.7 +/- 1.0% (ES=0.44)) and percooling (+9.9 +/- 1.9% (ES=0.40)) to improve exercise performance. A lower finishing Tc was found in precooling (38.9 degrees C) compared with control condition (39.1 degrees C, p=0.03), while Tc was comparable between conditions in percooling studies. No correlation between Tc and performance was found. We found significant differences between cooling strategies, with a combination of multiple techniques being most effective for precooling (p<0.01) and ice vest for percooling (p=0.02). Conclusions Cooling can significantly improve exercise performance in the heat. We found a comparable ES for precooling and percooling on exercise performance, while the type of cooling technique importantly impacts the effects. Precooling lowered the finishing core temperature, while there was no correlation between Tc and performance.