Article Text

Download PDFPDF
There is no ‘Swiss Army Knife’ of thermal indices: the importance of considering ‘why?’ and ‘for whom?’ when modelling heat stress in sport
  1. Andrew Grundstein1,
  2. Jennifer Vanos2
  1. 1 Department of Geography, University of Georgia, Athens, Georgia, USA
  2. 2 School of Sustainability, Arizona State University, Tempe, Arizona, USA
  1. Correspondence to Dr Andrew Grundstein, Geography, University of Georgia, Athens, GA 30602, USA; andrewg{at}

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.


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.

From simple to complex: the devil is in the details

A simple thermal index with few inputs might seem useful for clinical purposes. However, it is critical to understand the underlying assumptions …

View Full Text


  • Contributors AG conceived of the idea, JV and AG developed and wrote the editorial, JV developed the figure and supplemental table.

  • 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.

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

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.