Exercising in the Heat

9 ways to keep your summer workouts safe.

By Barbara Russi Sarnataro
WebMD Weight Loss Clinic - Feature

Reviewed By Louise Chang, MD

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.