Warm-weather workout: exercising when heat and humidity soar.

Hot, sweltering, and sticky weather may be perfect for a day at the beach. But if you're trying to exercise--whether to train for the Olympic Games or just for fitness and fun--it can present a real problem. Sometimes it can even be dangerous.

"Extreme heat can adversely affect everybody--the world-class athletes you'll be seeing in the Olympics, recreational athletes, and even the spectators," cautions David Martin, Ph.D., a Georgia State University physiologist, chair of Sports and Science for the U.S.A. Track and Field Association, and consulting physiologist for the Atlanta Olympic Games, where temperatures this July could reach a humid 100 degrees downtown. "It's vital that anybody planning to be out in severely hot weather should take the heat very, very seriously, particularly those who live and usually exercise in cooler climates," Martin says.

Below is some safety advice from Martin, mixed in with a few tried-and-trusted hot-weather training tips from Marc Varsano, a race walker from New York City, and Gwynneth Coogan, a marathon runner from Boulder, Colorado.

Physical Protection Against the Sun

Use appropriate sunscreen. Follow the recommended protection levels that come with the sunscreen. Wear a light-colored mesh hat (guys, watch out for that bald spot, which can get severely sunburned) and loose-fitting, lightweight, light-colored clothing. Wear sunglasses if the sun hurts your eyes.

Acclimation--Getting Used to the Heat

"It takes at least two weeks for the body to properly adjust to a significantly new climate," Martin explains. "For the recreational athlete who's preparing to exercise in a hot and sunny vacation spot, becoming acclimated can mean simply making sure you get out into even hazy sunlight as much as possible in the month or so leading up to your trip.

"You should also be aware of whether you're dealing with wet (humid) heat or dry heat. High humidity can put much more stress on the human body, since it hinders the evaporation of sweat--which is an important cooling mechanism in the human body," Martin says.

Varsano says he acclimates himself to hot-weather races by throwing on a few extra sweatshirts during winter training sessions in New York. "It doesn't take me long to get really hot, even on a winter day in Central Park," Varsano says. He begins using this technique about a month or so before the hot-weather race. "I don't do it for every session, because it slows down my time, and I need the psychological lift of seeing my time improve. I also vary my training, so that it isn't always necessary for me to be sweating like mad."

Varsano's technique is a reasonable way to become acclimated, Martin says. "If he were going to race in a humid heat, such as in Atlanta, then this is perfect, since he's creating a `little Atlanta' in his sweats."

Fluids

"Drink a lot, as much as you can. Never let yourself become thirsty, because by then it's often too late," Martin says. Keeping the body properly hydrated is vital for those exerting themselves in the heat, Martin says.

"I know I feel heavy and slow when I haven't had enough fluids before and during a race," says Coogan. Coogan says she's heard of extreme situations in which dehydrated distance runners have died during hot weather. "I pay very close attention to what my body is telling me," she says.

Cool water is the preferred drink, because the body can easily absorb it and put it to good use, Martin says. In a pinch, it's OK to take in other fluids such as Gatorade, Powerade--preferably those that have less than percent sugar, Martin says. Sugar slows down how quickly the body absorbs fluids. But again, try to drink before you feel thirsty. And get some cool water inside you as soon as you can. "The advantages of carrying a water bottle with you when you run seldom outweigh the disadvantages," says Martin, so try to stay within reasonable distance of a water supply.

Varsano says he's experienced discomfort when he didn't take in enough fluid during a long race, so now he'll take fluids whenever they are offered. "I also tend to begin hydrating the night before a race " Varsano says. While this doesn't affect his hydration level the following day, it does ensure that he isn't carrying any dehydration overnight Martin says. "If you try this and find yourself getting up at night to use the bathroom, then you're fully hydrated, and you should reduce or eliminate some of the water you're drinking before going to bed," Martin notes.

Best Time to Run

Even if you feel fairly well acclimated to sweltering conditions, you should try to schedule your exercise for mornings or early evenings, when the heat and sunshine are diminished Martin advises. Varsano says that if he knows he's scheduled to race in the midday heat, then it helps him to train in it, too.

Intensity, Rest, Shade, and Overdoing It

Recreational and professional athletes like to maintain their times and intensity even in dangerously hot weather. But this is a mistake, Martin says. "It's especially important for the recreational athlete to be aware of light-headedness, dizziness, leg cramps, unusual shortness of breath, and general discomfort. It might be the start of heat stress or heat stroke," Martin says. Slow down or make an unscheduled stop for rest, shade, and cool fluids. You should also take any sunburn you notice seriously.

Surviving Nonathletic Activities in the Heat

Spectators as well as athletes at this year's Olympic Games will have to be careful in the heat. Olympic Games organizers are distributing information to ticket buyers on how to deal with the hot weather. "Walking around or just sitting for long periods in the heat can cause heat-related problems" that can result in heat stroke and other ailments, Martin says. "Don't underestimate the exertion of simply being out in the sun for a long period. Pay attention to your fluid intake and what your body is telling you with regard to rest and shade."

Vary Your Training

Exercisers uncomfortable in or not properly acclimated to the heat can try different forms of exercise. Instead of running, for instance, you could try cycling, which allows you to bring your own fluid and creates a cooling breeze. Swimming is another good alternative.

RELATED ARTICLE: A Primer on Hot-Weather Exercise

* Try to limit physical exertion to the morning or late afternoon, when it's cooler.

* Be aware of stomach or leg cramps, weakness, dizziness, disorientation, and confusion. These are symptoms that you are overdoing it.

* Plan the more physical of your activities for later on in your vacation, to give your body at least some time to become acclimated to the hotter temperatures.

* Consider cycling, rather than walking long distances. Cycling allows you to rest, and you can carry fluids with you.

* Resist the temptation to dress fashionably "baggy" and layered when exercising or sightseeing in the heat. Also, avoid waterproof and wind-resistant clothing, because it hinders sweating and cooling. Instead,