Exercising in the Heat

9 ways to keep your summer workouts safe.

Reviewed by Brunilda Nazario, MD on June 25, 2008
From the WebMD Archives

During the long, cold days of winter, we long for summer exercise: soccer in the park, a bike ride along the river, a hike in the mountains, or just a day in the garden. But when the dog days of summer actually arrive, it’s important to be prepared. Exercising in the heat can be risky if you aren't careful.

Personal trainer and marathoner Carla Branch saw the danger of heat and dehydration while running a marathon in Tupelo, Miss., in August a few years back. It was the weekend before Labor Day, Branch recalls.

"It was a hot, humid day, and we were running on country roads, and the aid stations were about five miles apart," she says. "There just wasn’t enough support."

Because she planned ahead and placed extra water along the route, Branch was fine. But many racers weren’t so lucky. "My friend started getting dizzy and staggering, and another guy had to be put on IV [fluid] because of dehydration," she says.

A large percentage of people couldn’t finish the race, says Branch.

For you, exercising in the heat may not mean running 26.2 miles. But even if you’re not planning to run a marathon, you want to be smart before embarking on a summer workout.

When taking on summer exercise outdoors, says Argyle, Texas, exercise physiologist Jaime Roberts, "we need to be aware of the increase in heat and humidity."

Typically, says Roberts, our bodies are warmer than the environment. When that begins to change, our muscles regulate heat by releasing sweat, which allows the body to cool itself. But when the body is sweating, it’s losing fluid, she says.

Heat exhaustion and heat stroke, dangerous side effects of overdoing summer exercise, come when the body can no longer sustain the pace, the heat, the humidity, or the loss of fluid.

"The body cools off by sweating," says Roberts, "and as long as you remain hydrated, the body is able to cool itself off."

When you become dehydrated, the problems start.

"If the body can no longer cool itself," Roberts tells WebMD, "it starts storing heat inside. The core temperature begins to rise and you put your internal organs and central nervous system at risk."

Signs of heat exhaustion include general fatigue, weakness, nausea, dizziness, muscle cramps, and an increase in body temperature. Temperatures above 104, an inability to sweat, acute respiratory distress, and loss of consciousness can be signs of heat stroke, which is much more severe and can lead to death.

This doesn't mean you have to abandon your quest for a great summer workout. Just follow these nine guidelines to exercise smart in the heat. But make sure to talk to your doctor about starting an exercise regimen and issues about heat and hydration.

Summer Exercise Tip No. 1: Acclimate Yourself

"When the weather warms, you need to be acclimated to the temperature change," says William O. Roberts, MD, FACSM, a family medicine and sports medicine doctor at the University of Minnesota’s Phalen Village Clinic. "Expose yourself regularly."

Branch tells her clients it can take up to 14 days to adjust to temperature changes. When clients are preparing for an event that will take place in the heat of the day, Branch coaches them to be active in the heat ahead of time: "They have to try to get out in the middle of the day when it’s hot and exercise in order to acclimate to the conditions for the event."

But remember, if you are just doing routine exercise, it is better to exercise outside when it is cooler, such as the early morning or evening. (See more about this in tip No. 5.)

Summer Exercise Tip No. 2: Stay Hydrated

When it comes to summer exercise, all our experts agree that the biggest concern is hydration.

Suzanne Girard Eberle, author and sports dietitian in Portland, Ore., says that if you come back from a summer workout 1 to 2 pounds lighter, you’ve got to do a better job keeping up with hydration. You lose 2 1/2 cups of water per pound of body weight lost, she says.

If your urine is the color of lemonade, says Roberts, you’re well hydrated. If it’s darker in color then you may be dehydrated.

"If you’re going four to six hours without eliminating, you’re not hydrated enough," adds Eberle, a former elite runner and author of Endurance Sports Nutrition.

To maintain good hydration for a moderate summer workout, Roberts recommends drinking 20 ounces of water two hours before exercise, at least 8 ounces of water shortly before getting out in the heat, and then a gulp every 15 to 20 minutes during exercise. Make sure to talk to your doctor about specific fluid intake when you exercise.

To stay better hydrated, says Eberle, drink fluids with food throughout the day.

Summer Exercise Tip No. 3: Slow Down

When the temperature hits the 90s, don’t expect to go out and set a personal record, says Roberts.

"If it’s hotter than you’re used to, cut the pace back or cut the exposure back," he says. "Don’t try to do the same pace you did the day before."

Be careful about trying to keep up with friends who are more fit or have a higher tolerance for heat as well, says Eberle.

"Just realize you are going to be slower," says Eberle, "and particularly on humid days, it’s going to take you longer to finish."

Summer Exercise Tip No. 4: Wear Light, Breathable Clothing

Lightweight fabrics that wick away sweat are best for exercising in the heat, says Eberle. Clothes should also be light in color in order to reflect the sun.

"One common problem is people overdress," she says. "They cover up the working muscles in the legs, which generates a lot of heat."

Sunscreen is also important when you exercise outdoors.

"A well-ventilated hat with a brim and some lightweight sunglasses can [protect your face] and help prevent headaches," says Eberle.

If your summer workout involves wearing a protective helmet, adds Roberts, remove it during rest periods to allow your head to breathe and cool off.

Summer Exercise Tip No. 5: Exercise Early or Late

If possible, get out before 7 a.m. or after 6 p.m. to exercise in the summer months, says Roberts. This will add length to your day, and energy to your summer workout. Inevitably, heat and humidity will slow you down.

"In the worst part of summer, especially if you just want to exercise for health, do it in the gym if you can. Or get out early in the day or late in the evening," says Branch.

Summer Exercise Tip No. 6: Assess the Previous Day

It’s not enough to know how you feel right before going out to exercise in the heat, says Roberts.

"It’s very important with those who exercise regularly to take into account the physical activity, fluid ingestion, and diet of the previous day," she says. "You could be dehydrated or fatigued even prior to exercising," which could get you into trouble faster on a hot day, she says.

Summer Exercise Tip No. 7: Know the Route and Climate

It’s important to know your route and your climate, says Roberts.

"Make sure that there’s some shade along the way and that you’re not exposed to constant direct sunlight," she says.

Check the heat index for the relative humidity that day and plan accordingly, she says. Contain your summer exercise to the least hot and humid part of the day.

If you live in a dry climate, like the desert Southwest, says Roberts, remember that sweat evaporates quickly. You’re going to lose a lot more fluid exercising in the heat in Phoenix than Portland. And because it’s drying almost before you can see it, you don’t know how much fluid you’re losing.

Summer Exercise Tip No. 8: Consult Your Doctor or Pharmacist

Many medications -- both prescription and over-the-counter -- can intensify the effects of heat-related illnesses, says Roberts. Decongestants, appetite suppressants, antihistamines, antihypertensives, and antidepressants can hasten dehydration and decrease the body’s ability to recognize danger.

Even diuretics like caffeine and alcohol, when consumed before exercising in the heat, can accelerate the effects of dehydration, says Roberts.

Summer Exercise Tip No. 9: Use Common Sense

Don’t choose a hot summer day to try your hand at rock climbing or in-line skating for the first time.

"You shouldn’t start doing something brand new if it’s really hot," says Roberts, "even if it’s just for a half an hour."

When you don’t know what to expect or how your body will take to the activity, it’s best to save it for a cooler, more forgiving day, he says.

"The biggest thing with heat and exercise," says Branch, "is common sense. If you’re feeling bad, you need to get inside, get your core temperature down. Even if you are in an event, it’s just not worth it. You want to live to run another day."

Show Sources

SOURCES: Carla Branch, personal trainer, Little Rock, Ark. Jaime Roberts, MS, exercise physiologist; personal trainer, Argyle, Texas. William O. Roberts, MD, FACSM, family and sports medicine doctor, University of Minnesota’s Phalen Village Clinic, St. Paul. Suzanne Girard Eberle, MS, RD, CSSD, sports dietitian; nutrition coach; author, Endurance Sports Nutrition.

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