Validation of upper thermal thresholds for outdoor sports using thermal physiology modelling

Abstract Objectives : To validate the upper thresholds of the thermal safety guidelines for multiple outdoor sports in terms of heat illness risk. Methods: The reproducibility of the joint system thermoregulation model (JOS-3) of core temperature has been validated for 18 sports experiments (n=213) and 11 general exercise experiments (n=121) using the Bland–Altman analysis. Core temperatures were predicted using the JOS-3 in conditions corresponding to the upper thresholds, and if the 90th–99.7 th percentile core temperature value (corresponding to 0.3%–10% of the participants) exceeded 40℃, the thresholds were judged as potentially hazardous. Revisions are proposed for sports with potentially hazardous thresholds. Results: The JOS-3 could simulate core temperature increases in most experiments (27/29) for six sports and general exercises with an accuracy of 0.5℃, provided that systematic errors were corrected. The current upper thresholds for marathons, triathlons, and football are potentially hazardous. Based on our model settings, the upper thresholds should be revised as follows for participants' safety, depending on the specified percentiles: Football: revise from wet bulb globe temperature (WBGT) 32℃ to 29–31℃ or not revise. Marathon: revise from WBGT 28℃ to 24–27℃. Triathlon: revise from WBGT 32.2℃ to 23–26℃. Conclusion: The upper thresholds for marathons, triathlons, and football are potentially hazardous and revising the thresholds should be considered. The thermo-physiological model approach can be applied to heat illness risk assessment in sports while avoiding logistical and ethical difficulties, and can potentially contribute to such assessments in various sports and conditions.