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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
  1. Sofia Thorsson1,
  2. David Rayner1,
  3. Gunnar Palm1,
  4. Fredrik Lindberg1,
  5. Eric Carlström2,3,
  6. Mats Börjesson4,5,
  7. Finn Nilson6,
  8. Amir Khorram-Manesh7,
  9. Björn Holmer1
  1. 1Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden
  2. 2Institute of Health Sciences, University of Gothenburg Sahlgrenska Academy, Goteborg, Sweden
  3. 3Department of Business, Historical and Social Science, University of South-Eastern Norway - Campus Vestfold Library, Borre, Vestfold, Norway
  4. 4Department of Molecular and Clinical Medicine, University of Gothenburg Institute of Medicine, Gothenburg, Sweden
  5. 5Center for Health and Performance, University of Gothenburg Sahlgrenska Academy, Gothenburg, Sweden
  6. 6Department of Life and Environmental Sciences, Karlstad University, Karlstad, Sweden
  7. 7Department of Surgery, Institute of Clinical Sciences, University of Gothenburg Sahlgrenska Academy, Gothenburg, Sweden
  1. Correspondence to Professor Sofia Thorsson, Department of Earth Sciences, University of Gothenburg, Gothenburg SE-405 30, Sweden; sofia.thorsson{at}


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.

  • running
  • exertional heat stress
  • marathon

Statistics from


  • Contributors ST led the study. All authors, ST, GP, FL, DR, EC, MB, FN, AK-M and BH conceived the study and provided input on the study design. EC and AK-M selected medical records for the study period. GP, FL and DR collected and processed the metrological data. FL, GP and ST calculated the thermal indices. DR, ST and BH analysed the data. ST drafted the manuscript. All authors edited and approved the final version of the paper.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Patient consent for publication Not required.

  • Ethics approval Ethical consent was secured from the Regional Ethics Committee in Gothenburg (Ref. 003–17).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement 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.

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