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Keep Your Fitness Cool: Exercising in the Heat

Try these tips to work out safely when it's hot outside
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WebMD Weight Loss Clinic-Feature

In Phoenix, locals call it a "cold snap" when the thermometer drops below 105 degrees. After spending time at a construction site, Arizona builder Albert Ayala found his head swimming and noticed he had stopped sweating. "I felt terrible," he recalls. He went home and a couple of hours later, experienced fierce muscle cramps. "I thought I knew heat," he says, "but it got me."

"It can happen to anyone," says Andrea M. McCauley, director of communication for the American Red Cross in the Phoenix area. Although becoming acclimated gradually to heat helps (in Phoenix, they say if you can get through one summer, you won't notice the heat as much), acclimation is not the whole answer.

How Hot Is Hot?

"When should you worry about exercising in the heat?" asks William O. Roberts, MD, a sports medicine specialist with MinnHealth in White Bear Lake, Minn., (not in a desert, notice -- this can happen anywhere). "That's a moving target. A lot depends on the humidity. With no acclimation, 70 degrees with high humidity can be dangerous. Your sweat can't evaporate."

Heat, Roberts repeats, is not something you can instinctively gauge. "People often don't realize how hot and humid it is until they are already in trouble."

If the body cannot carry the heat given off by exercising muscles to the surface of the body fast enough -- and once it's there, if the surrounding air is not cooler or evaporating sweat does not cool the body -- one's innards literally stew, destroying and shutting down organ systems. It's not a matter of discipline or will, it's a matter of heat exchange -- physics and physiology, not physical endurance.

Symptoms of Trouble

The most common symptoms of heat illness are nausea, vomiting, headache, weakness, or an altered mental state (confused, raving, aggressive, rambling incoherently). Body temperature can spike up to 105 degrees or more (110 to 114 degrees is not unknown). If the sweating mechanism shuts down as it did in Albert's case, over time the body loses all hope of cooling itself and the brain and other organs begin to "cook." Heat stroke is the term for this latter condition and can result in death.

But it's not that simple. "I usually don't want to say heat exhaustion is a first stage of heat stroke or that it can go from one to the other," Roberts says. "They are two different things. You can get exercise exhaustion in the heat, but it's usually from the exercise not the heat."

Giving it a name is not that important. "You may suddenly get tired, sick, headachy, thirsty, or faint," sums up McCauley.

Hydration Not the Whole Answer

The most common piece of advice about exercising in the heat is drink, drink, drink -- water, not caffeine-loaded sodas or beer. Roberts says you can get heat exhaustion even if you are hydrated, though. He recommends determining your sweat rate instead and replacing that, without overdoing it.

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