Combining extreme heat with exercise increases the risks of exertional heat illness, impairs performance and imposes thermoregulatory strain on athletes.1 What is the best way to monitor heat stress and strain in athletes? Wet bulb globe temperature (WBGT)—a direct environmental measure—coupled with activity modification, has long been used in sports, occupational safety and the military.2 Because of its longevity, it has well-known benefits (eg, simple to calculate/measure; integrates multiple weather variables) and limitations (eg, underestimation of stress of restricted evaporation; poor incorporation of clothing/adjustment factors).3 4 Practical decisions, such as cancelling an event or implementing countermeasures for heat, depend not only on the environmental conditions, but on the nature and length of the activity itself (eg, marathon vs beach volleyball), clothing and athlete anatomical characteristics. In recent decades, additional heat metrics that are derived from human energy balance models (eg, the physiological equivalent temperature (PET) and the Universal Thermal Climate Index (UTCI)) have been introduced and increasingly applied, even for sporting events.5 These more comprehensive heat indices are designed to provide more meteorologically dynamic outputs to predict heat stress. However, they have their own limitations for sporting applications due to simplified and non-modifiable physiological/behavioural factors that are not sport-specific in their available formats. Does our field of sport-related environmental physiology need to expand the arsenal of heat monitoring tools-both measurements and models-beyond indices that have been simplified for general applications? This editorial calls attention to the considerations and the potential misuse of thermal indices applied in outdoor sport settings.
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