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Try these tips to work out safely when it's hot outside

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.

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