Impact of different climatic conditions on peak core temperature of elite athletes during exercise in the heat: a Thermo Tokyo simulation study

OBJECTIVES: To evaluate how separate and combined climatic parameters affect peak core temperature during exercise in the heat using computer simulations fed with individual data. METHODS: The impact of eight environmental conditions on rectal temperature (T(re)) was determined for exercise under heat stress using the Fiala-thermal-Physiology-and-Comfort simulation model. Variations in ambient temperature (T(a)±6°C), relative humidity (RH±15%) and solar radiation (SR+921 W/m(2)) were assessed in isolation and combination (worst-case/best-case scenarios) and compared with baseline (T(a)32°C, RH 75%, SR 0 W/m(2)). The simulation model was fed with personal, anthropometric and individual exercise characteristics. RESULTS: 54 athletes exercised for 46±10 min at baseline conditions and achieved a peak core temperature of 38.9±0.5°C. Simulations at a higher T(a) (38°C) and SR (921 W/m(2)) resulted in a higher peak T(re) compared with baseline (+0.6±0.3°C and +0.5±0.2°C, respectively), whereas a higher RH (90%) hardly affected peak T(re) (+0.1±0.1°C). A lower T(a) (26°C) and RH (60%) reduced peak T(re) by −0.4±0.2°C and a minor −0.1±0.1°C, respectively. The worst-case simulation yielded a 1.5±0.4°C higher T(re) than baseline and 2.0±0.7°C higher than the best-case condition. CONCLUSION: Combined unfavourable climatic conditions produce a greater increase in peak core temperature than the sum of its parts in elite athletes exercising in the heat.