Background: A majority of high profile international sporting events, including the coming 2020 Tokyo Olympics, are held in warm and humid conditions. When exercising in the heat, the rapid rise of body core temperature ( T c ) often results in an impairment of exercise capacity and performance. As such, heat mitigation strategies such as aerobic fitness (AF), heat acclimation/acclimatization (HA), pre-exercise cooling (PC) and fluid ingestion (FI) can be introduced to counteract the debilitating effects of heat strain. We performed a meta-analysis to evaluate the effectiveness of these mitigation strategies using magnitude-based inferences. Methods: A computer-based literature search was performed up to 24 July 2018 using the electronic databases: PubMed, SPORTDiscus and Google Scholar. After applying a set of inclusion and exclusion criteria, a total of 118 studies were selected for evaluation. Each study was assessed according to the intervention's ability to lower T c before exercise, attenuate the rise of T c during exercise, extend T c at the end of exercise and improve endurance. Weighted averages of Hedges' g were calculated for each strategy. Results: PC ( g = 1.01) was most effective in lowering T c before exercise, followed by HA ( g = 0.72), AF ( g = 0.65), and FI ( g = 0.11). FI ( g = 0.70) was most effective in attenuating the rate of rise of T c , followed by HA ( g = 0.35), AF ( g = −0.03) and PC ( g = −0.46). In extending T c at the end of exercise, AF ( g = 1.11) was most influential, followed by HA ( g = −0.28), PC ( g = −0.29) and FI ( g = −0.50). In combination, AF ( g = 0.45) was most effective at favorably altering T c , followed by HA ( g = 0.42), PC ( g = 0.11) and FI ( g = 0.09). AF (1.01) was also found to be most effective in improving endurance, followed by HA (0.19), FI (−0.16) and PC (−0.20). Conclusion: AF was found to be the most effective in terms of a strategy's ability to favorably alter T c , followed by HA, PC and lastly, FI. Interestingly, a similar ranking was observed in improving endurance, with AF being the most effective, followed by HA, FI, and PC. Knowledge gained from this meta-analysis will be useful in allowing athletes, coaches and sport scientists to mak...

Exercising in the heat often results in an excessive increase in body core temperature, which can be detrimental to health and endurance performance. Research in recent years has shifted toward the optimum temperature at which drinks should be ingested. The ingestion of cold drinks can reduce body core temperature before exercise but less so during exercise. Temperature of drinks does not seem to have an effect on the rate of gastric emptying and intestinal absorption. Manipulating the specific heat capacity of a solution can further induce a greater heat sink. Ingestion of ice slurry exploits the additional energy required to convert the solution from ice to water (enthalpy of fusion). Body core temperature is occasionally observed to be higher at the point of exhaustion with the ingestion of ice slurry. There is growing evidence to suggest that ingesting ice slurry is an effective and practical strategy to prevent excessive rise of body core temperature and improve endurance performance. This information is especially important when only a fixed amount of fluid is allowed to be carried, often seen in some ultra-endurance events and military operations. Future studies should evaluate the efficacy of ice slurry in various exercise and environmental conditions.The rise in body core temperature to a high level, known as hyperthermia, is related to the body heat storage that occurs from either an increase in metabolic heat production or a decrease in heat loss. The classic paper by Nielsen (1938) showed that this elevation in body core temperature during steady-state exercise was proportional to metabolic rate and independent of ambient temperature from 5 to 30°C, later known as the prescriptive zone -a range of conditions in which the increase of body core temperature during exercise is independent of the environment (Lind, 1963).The debilitating effects of heat stress are well known and history has provided many examples of heat illness and death caused by heat stress (see Leithead & Lind, 1964;Parsons, 2003 for a review of some cases). The negative effects of heat stress on endurance capacity are also well documented in several well-controlled laboratory investigations (Febbraio et al., 1994; Galloway & Maughan, 1997;Parkin et al., 1999). The combination of exercise and heat strain results in competition between the skeletal muscle and skin for a limited blood flow (Rowell, 1974), i.e., blood required to provide oxygen and to remove metabolic waste products and blood required to promote heat loss at the skin. Extensive literature has affirmed that heat stress combined with exercise imposes severe strain on thermoregulatory and cardiovascular systems, as indicated by hyperthermia, dehydration, reduced work capacity, and occasionally, circulatory collapse (Brengelmann, 1983; GonzalezAlonso, 1998; Kay & Marino, 2000;Burke, 2001;Coris et al., 2004;Maughan & Shirreffs, 2004).To date, several interventions such as heat acclimation/acclimatization (Nielsen et al., 1993;Moran et al., 1996;Nielsen, 1998;Shapiro et al.,...

There is limited information on the ingestion of cold drinks after exercise. We investigated the thermoregulatory effects of ingesting drinks at 4°C (COLD) or 28°C (WARM) during work-rest cycles in the heat. On 2 separate occasions, 8 healthy males walked on the treadmill for 2 cycles (45 min work; 15 min rest) at 5.5 km/h with 7.5% gradient. Two aliquots of 400 mL of plain water at either 4°C or 28°C were consumed during each rest period. Rectal temperature (T re ), skin temperature (T sk ), heart rate and subjective ratings were measured. Mean decrease in T re at the end of the final work-rest cycle was greater after the ingestion of COLD drinks (0.5±0.2°C) than WARM drinks (0.3±0.2°C; P<0.05). Rate of decrease in T sk was greater after ingestion of COLD drinks during the first rest period (P<0.01). Mean heart rate was lower after ingesting COLD drinks (P<0.05). Ratings of thermal sensation were lower during the second rest phase after ingestion of COLD drinks (P<0.05). The ingestion of COLD drinks after exercise resulted in a lesser than expected reduction of T re . Nevertheless, the reduction in T re implies a potential for improved work tolerance during military and occupational settings in the heat.

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