Optimizing Ice Slurry Ingestion for Endurance Performance in the Heat: A Meta-Analysis

Introduction Environmental heat has been well documented to impact negatively athletes during high-intensity, long duration competitions. Exercising in high temperature and/or high humidity decreases time to exhaustion, increases heat storage, and reduces endurance performance (Nybo, Rasmussen, & Sawka, 2014). For elite endurance athletes competing at the highest level, performance in the heat has been shown to be impaired by ~3% compared to thermoneutral competition conditions (Guy, Deakin, Edwards, Miller, & Pyne, 2015). Considering the smallest worthwhile variation in elite endurance runners is less than 2.5% (Hopkins & Hewson, 2001), strategies that could eff ectively mitigate the negative infl uences of heat are highly relevant to the medal perspective for elite athletes competing in hot and humid environments. Not surprisingly, there is an ever-increasing interest in active cooling strategies for high-intensity sports that are of a long duration in challenging environments. Successful interventions include cold water immersion, cooling vests, cold/ ice drinks that can be applied as pre-cooling and/or during exercise (Bongers, Th ijssen, Veltmeijer, Hopman, & Eijsvogels, 2015). Active cooling strategies are recognized by both practitioners and sports scientists for the successful participation in endurance exercise in the heat. Interestingly, ice slurry ingestion has been reported to be the most prevalent cooling strategy amongst elite athletes preparing for the 2015 World Athletics Championships (Periard et al., 2017). While the specifi c reason for the popularity of ice slurry ingestion amongst elite athletes is not known, one of the possible reasons could be that ice slurry ingestion represents an eff ective yet practical intervention for fi eld applications. When employed as a pre-cooling intervention, ice slurry ingestion could eff ectively reduce core temperature at the commencement of exercise and, such eff ect could be carried over during the early stage of exercise, thus acting as a heat sink in challenging environments (Naito, Iribe, & Ogaki, 2017; Siegel et al., 2010). It has been reported Abstract