Modeling thermoregulatory responses during high-intensity exercise in warm environments.

The Six Cylinder Thermoregulatory Model (SCTM) has been validated thoroughly for resting humans. This type of modeling is helpful to predict and develop guidance for safe performance of work and recreational activities. In the context of a warming global climate, updating the accuracy of the model for intense exercise in warm environments will help a wide range of individuals in athletic, recreational and military settings. Three sets of previously collected data were used to determine SCTM accuracy. Dataset 1: two groups (large (LG) 91.5 kg and small (SM) 67.7 kg) of individuals performed 60 minutes of semi-recumbent cycling in temperate conditions (25.1°C) at metabolic rates of 570 to 700 W. Dataset 2: two LG (100 kg) and SM (65.8 kg) groups performed 60 minutes of semi-recumbent cycling in warm/hot environmental conditions (36.2°C) at metabolic rates of 590 to 680 W. Dataset 3: seven volunteers completed 8 km track trials (~ 30 minutes) in cool (17°C) and warm (30°C) environments. The volunteers' metabolic rates were estimated to be 1268 W and 1166 W, respectively. For all data sets, SCTM-predicted core temperatures were found to be similar to the observed core temperatures. The root mean square deviations (RMSD) ranged from 0.06 to 0.46 °C with an average of 0.2 °C deviation, which is less than the acceptance threshold of 0.5°C. Thus, the present validation shows that SCTM predicts core temperatures with acceptable accuracy during intense exercise in warm environments and successfully captures core temperature differences between large and small individuals.