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.

Is it too hot outside to do exercise?

There’s no precise temperature at which it becomes unsafe to exercise. According to Melissa Kendter (Perkasie, Pa.), a functional trainer and personal trainer who is also a running coach and functional training specialist, it all comes down to the individual factors.

“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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Over weeks of exercise outdoors, you may find your upper temperature threshold changing. Kendter, for example, says that she must reduce her marathon training early in summer to adjust to the higher temperatures 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. In order for your body to adjust, she suggests that you do two to four weeks worth of slower and less intense exercises.

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. Any exercise that you can perform slowly and mindfully on hot days is suitable, such as yoga, slow jogging, leisurely biking, or walking in the shade of a forest. Whatever you do, you should move slower than in 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.”

Kendter or any other expert may also suggest these tips:

  • Sweat-wicking, light-weight clothes are better for airflow
  • Get hydrated well before you start your exercise. You can also bring water with you to drink afterward.
  • If you’re running or biking, look for shaded routes, or do a HIIT workout in a shaded area
  • Wear a hat, even if you’ll be under tree cover
  • Plan to relocate indoors in the event of extreme heat and humidity

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

How can you recognize heat-related sickness?

The severity of heat-related illnesses can vary from mild to severe. The mildest symptoms, such as rashes and cramps are at the low end. Heat exhaustion is the most severe. 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. Heat stroke is when someone’s skin becomes dry and hot and stops sweating. You may experience a rapid heart beat and significant temperature rises. They are also more likely to experience severe symptoms, such as nausea, vomiting, brain damage, or seizures.

What can you do when you begin to heat up?

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 recommends taking your socks off and sprinkling cold water on your neck and face.

Batten suggests that anyone who is keen to exercise in heat should prioritize preventing heat-related illness. “Then you can enjoy your workout instead of putting your health at risk.”

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