%0 Journal Article %A Sofia Thorsson %A David Rayner %A Gunnar Palm %A Fredrik Lindberg %A Eric Carlström %A Mats Börjesson %A Finn Nilson %A Amir Khorram-Manesh %A Björn Holmer %T Is Physiological Equivalent Temperature (PET) a superior screening tool for heat stress risk than Wet-Bulb Globe Temperature (WBGT) index? Eight years of data from the Gothenburg half marathon %D 2021 %R 10.1136/bjsports-2019-100632 %J British Journal of Sports Medicine %P 825-830 %V 55 %N 15 %X Background The Wet-Bulb Globe Temperature (WBGT) index is a common tool to screen for heat stress for sporting events. However, the index has a number of limitations. Rational indices, such as the physiological equivalent temperature (PET) and Universal Thermal Climate Index (UTCI), are potential alternatives.Aim To identify the thermal index that best predicts ambulance-required assistances and collapses during a city half marathon.Methods Eight years (2010–2017) of meteorological and ambulance transport data, including medical records, from Gothenburg’s half-marathon were used to analyse associations between WBGT, PET and UTCI and the rates of ambulance-required assistances and collapses. All associations were evaluated by Monte-Carlo simulations and leave-one-out-cross-validation.Results The PET index showed the strongest correlation with both the rate of ambulance-required assistances (R2=0.72, p=0.008) and collapses (R2=0.71, p=0.008), followed by the UTCI (R2=0.64, p=0.017; R2=0.64, p=0.017) whereas the WBGT index showed substantially poorer correlations (R2=0.56, p=0.031; R2=0.56, p=0.033). PET stages of stress, match the rates of collapses better that the WBGT flag colour warning. Compared with the PET, the WBGT underestimates heat stress, especially at high radiant heat load. The rate of collapses increases with increasing heat stress; large increase from the day before the race seems to have an impact of the rate of collapses.Conclusion We contend that the PET is a better predictor of collapses during a half marathon than the WBGT. We call for further investigation of PET as a screening tool alongside WBGT.Data may be obtained from a third party and are not publicly available. The data are based on ambulance patient records and registers from the Gothenburg half marathon organisation. According to the ethical permission, deidentified data can be shared to other researchers involved in a linked study e.g. for comparative reasons. The data can be obtained from the first author, ST or EC (coauthor). There is no time limit on the availability of the data. %U https://bjsm.bmj.com/content/bjsports/55/15/825.full.pdf