Slower cyclists and higher temperatures are associated with illnesses during a 109km cycling event

August 11, 2021

News & Resources

Slower cyclists and higher temperatures are associated with illnesses during a 109km cycling event

With increased awareness of the health benefits of exercise, the participation in so-called “mass community-based endurance events”, such as the Cape Town Cycle Tour, is becoming popular.

And while physical activity is encouraged, these prolonged moderate- or high-intensity exercise events come with an increased risk of exercise-related illness and other medical complications.  Identifying which illnesses are commonly suffered by athletes, along with their respective risk factors (i.e. behaviours, characteristics or exposures that increase the likelihood of a person developing a disease or health disorder/complication), is important as this is the first step to design and implement specific illness prevention programs and better prepare medical teams and facilities on race day.  

Researchers at SEMLI (the Sport, Exercise Medicine and Lifestyle Institute at the University of Pretoria) recently set out to identify what these risk factors are, that could increase the likelihood of a cyclist getting ill during an endurance event. They found that a slower cycling speed and warmer, more humid environmental conditions were associated with illness-related medical encounters during the Cape Town Cycle Tour. Although they did not investigate the reasons for the association between slower cycling speed and risk of illness, they do speculate that slower cycling speed may be associated with suboptimal race preparation, less experience, or perhaps an underlying acute or chronic illness. They suggest that these, and other factors, be explored in future studies. A unique aspect to this study was that each participant’s environmental exposure was calculated using individual wet-bulb globe temperature (aiWBGT) measurements taken along the route for the duration of the race. This is important in an event such as the Cape Town Cycle Tour, where there is a staggered start, and participants can take up to 7 hours to finish. The researchers recommend that individualized environmental exposure, rather than an average exposure for the entire starting field, is important and affects the risk of illness in cyclists. Previous research by this group has shown that fluid and electrolyte disorders, particularly dehydration, are the most common illness in this cycling event, accounting for just under 30% of all illness-related medical encounters.  The most recent research adds to this knowledge, and shows that exposure to a higher aiWBGT is associated with fluid and electrolyte medical complications. Previous studies in endurance athletes have found that fluid and electrolyte disorders are often associated with poor hydration habits and poor strategies for heat acclimatization.

This research has important applications, including assisting race medical teams to prepare for certain illness-related incidents on race day based on the profile of cyclists, and to design and implement illness prevention programs for these events, in order to reduce medical complications and make participation in physical activity safer.

Risk Factors for Illness-related Medical Encounters during Cycling: A Study in 102,251 Race Starters—SAFER XI.  Med. Sci. Sports Exerc, Vol. 53,No. 3, pp. 517–523, 2021


Summary written 7 April 2021 by Dr Jill Borresen, COO SEMLI