Whether you exercise indoors, on a trail, on a field, or at any other location, your body can overheat. Everyone who exercises — even high-level athletes in prime condition — should have a plan to prevent heat-related illness and be aware of the signs.
“Your body is built to cool itself while you exercise. But when you exercise in warmer temperatures, your body has to work harder to do that. Everyone’s tolerance to heat is going to be a little different, and your body needs to be trained and prepared for what you’re asking it to do,” says Sarah Eby, MD, PhD, a sports medicine specialist at Mass General Brigham and Spaulding Rehabilitation Network. “So when you are planning to exercise, especially when outdoor temperatures start to warm up, you need to start low, start slow, and ease into activity. Keep an eye on your body and how it’s doing, and don’t push it too much.”
“Heat-related illness is your body’s response to excessive heat, excessive sweating, and the associated dehydration and loss of salt. Your body is basically telling you that you need to cool off,” Dr. Eby says. “When you develop symptoms of heat-related illness, your internal body temperature could be rising. That affects cellular and organ function, and it can damage internal tissues.”
Heat-related illness is a continuum, Dr. Eby says, from mild and reversible symptoms to a medical emergency. The stages are:
The moment you notice any early signs of heat-related illness:
Dr. Eby cautions that you should seek immediate medical attention if you:
Of course, the best strategy is to avoid developing heat-related illness in the first place, Dr. Eby says. She offers several simple strategies for athletes at all levels.
It’s essential to drink plenty of fluids before, during, and after a workout — even if you don’t feel thirsty.
“Hydrate, hydrate, hydrate,” Dr. Eby says. “Many athletes may say, ‘I don't need anything.’ But it’s so important to make sure that you’re maintaining hydration for your health and your performance. Coaches, trainers, and parents can help. Make sure you have hydration available for athletes, and normalize that athletes need to be drinking.”
Dr. Eby and the American Council on Exercise suggest the following plan for hydration while you exercise:
Read more hydration tips for athletes.
According to Dr. Eby, when exercising in the heat, you should:
Heat index is a way of characterizing what the temperature outside actually feels like to the human body. It’s also sometimes called “apparent temperature” or “real feel.” Heat index takes into account relative humidity in addition to air temperature. Athletes, parents, coaches, and team administrators can use the heat index for sports decisions, to set heat guidelines for sports and other activities.
The National Weather Service offers a heat index calculator and chart. You can use the tools to calculate the heat index and determine whether it’s safe to be exercising in the heat.
There are general heat index guidelines for youth sports and other people in high-risk groups, such as older people. Those guidelines indicate that you should begin to use caution at a heat index of 80. When the heat index is 90 or higher, athletes can be at risk for heat-related illness.
Dr. Eby recommends that athletes use the heat index to better understand the way heat affects them. “Athletes and active individuals should also remember that heat index is calculated for the shade. Your body’s response to the exact same workout at the same heat index is going to be very different if that workout is primarily in the sun versus the shade. With that in mind, take a look at the heat index and then go and do your workout. See how you did and how you felt, and take that into consideration the next time you exercise in the heat.”
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