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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.

Journal article
Authors Sofia Thorsson
D.P. Rayner
Gunnar Palm
Fredrik Lindberg
Eric Carlström
Mats Börjesson
Finn Nilson
Amir Khorram-Manesh
Björn Holmer
Published in British journal of sports medicine
ISSN 1473-0480
Publication year 2020
Published at Institute of Clinical Sciences, Department of Surgery
Department of Earth Sciences
Institute of Neuroscience and Physiology
Institute of Health and Care Sciences
Language en
Keywords exertional heat stress; marathon; running.
Subject categories Environmental Health and Occupational Health, Public Health, Global Health, Social Medicine and Epidemiology, Sport and Fitness Sciences


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.To identify the thermal index that best predicts ambulance-required assistances and collapses during a city half marathon.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.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.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.

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