How to Exercise When It’s Really Hot Outside

For people in many parts of the U.S.—as well as large portions of the world—the phrase “record heat” has been a regular part of the recent forecast. While that doesn’t mean you have to move your favorite outdoor workout into the gym, you may need to do it a little differently. Here’s what experts recommend for staying safe and active outdoors.

How hot is too hot to exercise outside?

There’s no precise temperature at which it becomes unsafe to exercise. It comes down to individual factors, according to Melissa Kendter, a personal trainer at EvolveYou, running coach, and functional training specialist in Perkasie, Pa.

“This depends on how your body responds to heat, your fitness level, age, and any underlying conditions you might have such as cardiovascular disease or asthma,” she says. “If you have trouble breathing when it’s humid, for instance, your definition of ‘too hot’ will be a lower temperature than someone who feels fine.”

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Your personal upper temperature threshold can change as you adapt over weeks of outdoor workouts. For example, early in the summer, Kendter says she has to scale back on her marathon training in order to acclimate to higher heat and humidity. But those same temperatures later in the summer aren’t usually a problem because she’s more conditioned to deal with the heat. She suggests about two to four weeks of slower, less intense exercise in order to let your body adjust.

What’s the best exercise to do outside?

If you want to stay cool and still enjoy the outdoors, it’s tough to beat swimming as an activity, says Kendter, especially in a refreshingly chilly pool, lake, or ocean. Beyond that, any exercise you can do slowly and mindfully is appropriate for hot days, including yoga, jogging at an easy pace, a leisurely bike ride, or hiking in a shaded forest. No matter what you choose, make sure to move more slowly than you would during other seasons.

“Exercising when it’s hot is more about maintaining consistency than improving your performance,” she adds. “Your body will be working harder because of the heat, so now is not the time to push yourself.” Working out in the early morning or early evening is another good way to stay safe.

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“In many cases, heat exhaustion is very preventable,” says Dr. Casey Batten, director of primary care sports medicine at Cedars-Sinai Kerlan-Jobe Institute in Los Angeles. “The main strategy if you’re going to exercise outdoors is to be prepared, and that means dressing the right way, working out when it’s cooler, and staying hydrated.”

Here are other tips Kendter and other experts advise:

Another important recommendation: Stay aware of how you’re feeling, so you can detect any heat-related problems as soon as they start.

What are the warning signs of heat-related illness?

Heat-related illness can range from mild to serious. On the lower end of that spectrum are mild annoyances like rashes or cramps, and on the other end are heat exhaustion and heat stroke. Usually, when the body’s temperature regulation begins to sputter, heat exhaustion comes first; if it’s not addressed quickly, it becomes the more dangerous form of heat-related illness, heat stroke.

For people who exercise outdoors, the most common problem is heat exhaustion, a condition where your body overheats due to exposure to high temperatures and humidity, says Dr. Ali Mesiwala, a neurosurgeon and sports specialist at DISC Sports & Spine Center in Newport Beach, Calif. Your body is normally efficient at dealing with temperature fluctuations, but when it’s suffering from heat exhaustion, the body indicates that it’s having trouble adjusting, he says.

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For example, you shiver when it’s too cold, which is the body’s way of creating more warmth. With heat, you tend to sweat more—and when that blend of water and electrolytes dries, the evaporation process is what cools you down. Particularly if it’s very humid, this doesn’t work as well because you don’t dry off fast enough, Mesiwala says.

“In that case, your body may continue to sweat, but it doesn’t work to regulate your core temperature, and that’s when symptoms of heat exhaustion can become very pronounced,” he adds. Those symptoms can include sudden fatigue or weakness; thirst that doesn’t improve with hydration; cold, clammy skin; headache; dizziness or lightheadedness; a rapid heartbeat or pulse; and irritability or confusion.

If you don’t address heat exhaustion immediately—and especially if you continue to exercise—that may lead to the more threatening situation of heat stroke, Mesiwala says. When someone is experiencing heat stroke, the skin turns dry and hot, and they stop sweating. They may also have a significant spike in temperature and a more rapid heartbeat. There will also be higher risk of more serious symptoms like vomiting, loss of consciousness, slurred speech, and seizures.

What should you do if you start to overheat?

Signs of heat stroke need emergency attention, so if that’s occurring for you or someone else, call 911 or go to an emergency room. If it’s heat exhaustion, there are steps you can take to bring your core body temperature back where it should be.

First, stop working out. Get to a cool, shaded area—going inside to an air-conditioned space is best—and drink cool water or a sports drink in frequent sips. Mesiwala also suggests removing shoes and socks and splashing your face and neck with cold water.

Preventing heat-related illness should be a priority for everyone who wants to exercise outside in the heat, says Batten. “Then you can enjoy your workout instead of putting your health at risk.”