How to Exercise Safely in the Heat(How to Exercise Safely in the Heat)

As temperatures creep into the 90s and beyond, dehydration and heat exhaustion while exercising become a very real—--and potentially dangerous--—threat. Exhibit A: Each year seems to generate a fresh crop of headlines about football players of all ages collapsing during preseason practice.

Competitive athletes aren't the only ones who can experience problems when the mercury and humidity start to peak. Even if they're in excellent shape, weekend warriors may find themselves suffering heat-related symptoms after a long run or even a day of lawn mowing and yard work.

"People get out there and…do a really hard workout," says Scott Anderson, a certified athletic trainer in Clearwater, Fla. "The sensible thing is to go slow, and work up progressively. …A lot of people even go indoors and cross-train if it's too hot."

Not everyone has access to a climate-controlled gym, however. If your only option is to exercise outdoors despite the torrid weather, you can take some steps to avoid problems such as dehydration, cramping, heat exhaustion, and—--because air quality gets worse on hot, muggy days—--breathing trouble.

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How heat and humidity take a toll

When your body gets overheated, its natural response is to sweat. And when that sweat evaporates off your skin, it lowers your body temperature.

But if the temperature or humidity is sky-high, this built-in cooling system can break down. Sweat doesn't evaporate properly because of all the moisture in the air, and your skin doesn't release body heat as effectively.

"You're still sweating, but it's not doing as much for your body temperature," says Michael F. Bergeron, PhD, director of the National Institute for Athletic Health & Performance at the Sanford University of South Dakota Medical Center, in Sioux Falls.

As your body temperature climbs, lightheadedness, dizziness, nausea, fatigue, and muscle cramps can result. All of these are signs of heat exhaustion. And if you don't cool off quickly--—by going into an air-conditioned building or drinking cold water, say--—heat exhaustion can sometimes turn into heat stroke.

Heat stroke occurs when your body temperature hits 105°. The condition can cause problems in the muscles, kidneys, liver, brain, and heart, and people with heat stroke often start to breathe quickly and behave erratically, Bergeron notes. If they don't get medical help and bring their body temperature down, they may even have a seizure or slip into a coma.

In extreme cases heat stroke can be deadly. If you or someone you're with start to experience the symptoms of heat stroke, seek medical attention immediately or call 911.

When is it safe to exercise outdoors?

It's important to watch the temperature, but the most relevant number you need to know before heading outdoors is the heat index, which takes humidity into account and represents how hot it feels.

The risk of muscle cramping and heat exhaustion rises as the heat index climbs above 90. Although less serious than heat exhaustion, cramping is dangerous, especially when you're dehydrated. "When you start cramping and don't have enough fuel in the tank, that can lead to something more serious, like pulling a muscle," Anderson says. When the index is higher than 100, heat stroke also becomes more likely.

In the Tampa Bay area, where Anderson conditions and trains high school football players, the index is almost always in the danger zone, and it's not uncommon for it to reach 105. It's really important to modify your exercise routine when the index is that high, Anderson says.

Anderson recommends scaling back the duration or intensity of your workouts once the hot weather hits. It takes about two weeks to get acclimated to exercising in the heat (especially if you're not in top shape to begin with), he says. After that period, you're free to gradually ramp back up.

When it's really hot out, Bergen advises, it's a good idea to take breaks more frequently, exercise in the shade whenever possible, and wear breathable and light-colored clothing.

Exercising in the heat is safe if you use common sense and follow some basic rules, Bergeron says. "As long as they're not working [out] too hard, someone who is well rested, hydrated, and nourished can tolerate pretty tough conditions," he says.