May 28, 2026Heat stress planning for endurance events
Ask the Expert: Lessons from major marathons
(Sponsored) Heat stress can leave a major impact on endurance events — impacting athletic performance, safety and operations. It’s crucial to know how to plan for, monitor and mitigate heat stress.
We sat down with Sam Cheuvront, lead physiologist at New Balance Sports Research Lab in Boston, who has an extensive background in sports science,
thermal physiology and sports nutrition. Previously working at the U.S. Army Research Institute of Environmental Medicine in the Thermal and Mountain Medicine Division for nearly 20 years, Cheuvront studied the effects of heat and hydration on military and health performance. Additionally, Cheuvront owns a sports science consulting company, working with sports beverage and apparel manufacturers to mitigate the risks athletes face while staying hydrated and cool during training and competition in the heat.
Why is heat stress planning important for endurance events?
Heat stress planning is essential for endurance events because heat stress increases physiological strain, resulting in reduced performance capacity and increased health risks. Without a plan, even elite athletes are susceptible and medical resources can become overwhelmed.
What risks do athletes face when competing in high heat?
Endurance sports require high rates of metabolism and the desire to compete against others or ourselves drives body heat storage, increasing our body’s temperature. We naturally balance heat production with heat losses when the air temperature around us is cooler and the air is drier. When the air is warmer and more humid, all forms of heat loss are reduced. High air temperatures and strong sun can even add to body heat storage, while extremely hot and humid conditions can prevent heat loss.
What are the key steps in building a heat mitigation plan before race day?
There are many factors to consider when building a heat risk mitigation plan for an endurance sports event. For heat stress mitigation, the WBGT is key.
For the event director, consider risks, operations, medical and communications:
• Create a heat safety and risk mitigation protocol
• Conduct a risk assessment — use historical weather patterns (ideally WBGT) x medical encounters, identify problem segments of an event and establish thresholds for operational changes
• Create a tiered system that communicates risk clearly
• Consider changes to start times, wave starts to reduce density, or a seasonal calendar shift
• Maintain appropriate event hydration infrastructure
• Provide ‘per cooling’ options if warranted
• Communicate risk to participants and spectators (WBGT)
• Ensure sufficient medical coverage and treatment facilities.
How are weather and heat conditions monitored during a race?
Monitoring heat conditions has evolved from relying on air temperature and humidity to using WBGT, which incorporates temperature, humidity, solar radiation and airflow. Sports medicine groups recommend WBGT-based flag systems, with 28°C commonly considered the upper limit for safe endurance competition. The best practice is to measure WBGT on location, but if that’s not possible, validated models can be used. WBGT forecasting is still in development, but it is possible. In place of a WBGT forecast, a reliably hot and humid forecast within 72 hours should trigger enhanced heat stress mitigation or contingency planning.
How can athletic trainers apply these lessons to their own teams or events?
For events looking to implement a heat mitigation strategy, the Kestrel 5400 Heat Stress Tracker delivers real-time WBGT measurements exactly where athletes are competing. Quick setup, built-in WBGT guidelines, and customizable alerts help staff stay ahead of changing conditions and make informed decisions to prevent heat illness.
Learn more about Kestrel at kestrelinstruments.com/prevent-heat-stress.
