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Research & development

Exercise in the heat: too hot or not too hot?
18 feb

Exercise in the heat: too hot or not too hot?

P. Hespel, Exercise Physiology Research Group, KU Leuven


The recent events at the Australian Open tennis championships, as well as the ongoing discussion about the organization of the World Cup football 2018 in Qatar, has rebooted the discussion as to whether it is justified to organize sports competitions in extremely hot environmental conditions. Clearly, during prolonged (>60min) exercise in the heat athletes are at risk to collapse due heat illnesses such as heat stroke or heat exhaustion. In the extreme heat, and particularly during heat in conjunction with high relative humidity, body cooling is dramatically impaired. In addition, as soon as the environmental temperature is higher than the skin temperature, the ambient heat contributes to body heating. This makes body temperature to rise abnormally. Given the possible development of malignant hyperthermia, it is pertinent to raise the question: ‘From what point on high temperature is incompatible with prolonged high-intensity exercise? Theoretically, competition should be canceled, or at least the scenario of the sporting event must be modified, as soon as heat stress becomes incompensable and thus induces a serious health risk for the competitors. Moreover, prevention also addresses the safety of umpires, officials, volunteers, and last but not least the spectators who also are being exposed to excessive heat.


Several major international sports science organizations have written clear-cut recommendations for maintaining safety during exercise in the heat. For the purpose of this blog, we refer to the position stand by Sports Medicine Australia. The guidelines state that in healthy individuals ‘exercise must be postponed to a cooler condition or simply canceled as soon as ambient temperature is 36°C in combination with a relative humidity of >30%.’ Well-acclimatized and fit individuals clearly are less at risk than non-acclimatized persons. Still, the excessive environmental conditions in recent major international competitions such as the 2013 Amgen Tour of California (cycling in 40°C and 53% relative humidity) or the Australian Open Championships (tennis in 43°C and 61% relative humidity) caused serious heat illness in a number of athletes. It is reasonable to state that the aforementioned conditions were not compatible with sports competition. So what to say about the World Cup Football in Qatar expected to be organized in the summer of 2020 at temperatures expected to be higher than 45°C.


Clearly at present there is a big gap between the decision making by the organizers of some major international sports competitions and the recommendations by expert international organizations in sports medicine. The commercial benefits of the event unfortunately often appear to get a higher priority than the health status of the athletes involved.


For detailed recommendations for safe exercise in the heat we refer to the following consensus statements:

- Sports Medicine Australia:
- American College of Sports Medicine:

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