Within-subject Variation of Thermoregulatory Responses during Repeated Exercise Bouts

Aim: To assess the within-subject variation of thermoregulatory responses during 2 consecutive 15-km road races. Secondly, we explored whether gastrointestinal temperature (TGI) data from the first race could improve our previously established predictive model for finish TGI in the second race. Methods: We measured TGI before and immediately after both races in 58 participants and determined correlation coefficients. Finish TGI in the second race was predicted using a linear regression analysis including age, BMI, pre-race fluid intake, TGI increase between baseline and the start of the race and finish TGI in the first race. Results: Under cool conditions (WBGT 11–12°C), TGI was comparable between both races at baseline (37.6±0.4°C vs. 37.9±0.4°C; p=0.24) and finish (39.4±0.6°C vs. 39.4±0.6°C; p=0.83). Finish TGI correlated significantly between both races (r=0.50; p<0.001). The predictive model (p<0.001) could predict 32.2% of the finish TGI in the second race (vs. 17.1% without finish TGI in race 1). Conclusion: Our findings demonstrate that the use of previously obtained thermoregulatory responses results in higher predictability of finish core body temperatures in future races, enabling better risk assessment for those athletes that are most likely to benefit from preventive measures

Incidence and predictors of exertional hyperthermia after a 15-km road race in cool environmental conditions

Objectives Current knowledge about the incidence and risk factors for exertional hyperthermia (core body temperature ≥40 °C) is predominantly based on military populations or small-sized studies in athletes. We assessed the incidence of exertional hyperthermia in 227 participants of a 15-km running race, and identified predictors for exertional hyperthermia. Design Observational study. Methods We measured intestinal core body temperature before and immediately after the race. To identify predictive factors of maximum core body temperature, we entered sex, age, BMI, post-finish dehydration, number of training weeks, fluid intake before and during the race, finish time, and core body temperature change during warming-up into a backward linear regression analysis. Additionally, two subgroups of hyperthermic and non-hyperthermic participants were compared. Results In a WBGT of 11 °C, core body temperature increased from 37.6 ± 0.4 °C at baseline to 37.8 ± 0.4 °C after warming-up, and 39.2 ± 0.7 °C at the finish. A total of 15% of all participants had exertional hyperthermia at the finish. Age, BMI, fluid intake before the race and the core body temperature change during warming-up significantly predicted maximal core body temperature (p < 0.001). Participants with hyperthermia at the finish line had a significantly greater core body temperature rise (p < 0.01) during the warming-up compared to non-hyperthermic peers, but similar race times (p = 0.46). Conclusions 15% of the recreational runners developed exertional hyperthermia, whilst core body temperature change during the warming-up was identified as strongest predictor for core body temperature at the finish. This study emphasizes that exertional hyperthermia is a common phenomenon in recreational athletes, and can be partially predicted

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°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°C) compared with control condition (39.1°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