Predicting the body core temperature of recreational athletes at the end of a 10 km self-paced run under environmental heat stress

New FindingsWhat is the central question of this study?The aim was to identify the factors predicting the body core temperature of athletes at the end of a 10 km self-paced run in a hot environment.What is the main finding and its importance?Hyperthermia in athletes subjected to self-paced running depends on several factors, highlighting the integrated control of core temperature during exercise under environmental heat stress. Five of the seven variables that significantly predicted core temperature are not invasive and, therefore, practical for use outside the laboratory environment: heart rate, sweat rate, wet-bulb globe temperature, running speed and maximal oxygen consumption. Measurement of body core temperature (T-core) is paramount to determining the thermoregulatory strain of athletes. However, standard measurement procedures of T-core are not practical for extended use outside the laboratory environment. Therefore, determining the factors that predict T-core during a self-paced run is crucial for creating more effective strategies to minimize the heat-induced impairment of endurance performance and reduce the occurrence of exertional heatstroke. The aim of this study was to identify the factors predicting T-core values attained at the end of a 10 km time trial (end-T-core) under environmental heat stress. Initially, we extracted data obtained from 75 recordings of recreationally trained men and women. Next, we ran hierarchical multiple linear regression analyses to understand the predictive power of the following variables: wet-bulb globe temperature, average running speed, initial T-core, body mass, differences between T-core and skin temperature (T-skin), sweat rate, maximal oxygen uptake, heart rate and change in body mass. Our data indicated that T-core increased continuously during exercise, attaining 39.6 +/- 0.5 degrees C (mean +/- SD) after 53.9 +/- 7.5 min of treadmill running. This end-T-core value was primarily predicted by heart rate, sweat rate, differences between T-core and T-skin, wet-bulb globe temperature, initial T-core, running speed and maximal oxygen uptake, in this order of importance (beta power values corresponded to 0.462, -0.395, 0.393, 0.327, 0.277, 0.244 and 0.228, respectively). In conclusion, several factors predict T-core in athletes subjected to self-paced running under environmental heat stress. Moreover, considering the conditions investigated, heart rate and sweat rate, two practical (non-invasive) variables, have the highest predictive power.