H2AHHHHHH! : WHEN EXERCISING IN THE SUMMER, AVOID THE MIDDAY SUN AND DRINK LOTS OF WATER.

Byline: Jenifer Hanrahan Daily News Staff Writer

He may be the best decathlete in the world, but it will take more than superior strength, strategy and concentration for Dan O'Brien to earn the gold at this summer's Olympics.

He'll need water, and lots of it.

The quest for greatness this summer may come down to a grueling contest over who can beat the heat. Temperatures in Atlanta are expected to swelter in the 90s - and that's not counting the miserable humidity, which is expected to hover around 60 to 70 percent.

In fact, during oppressively hot Olympic Trials in Georgia last month, O'Brien and other decathletes couldn't drink water fast enough - so they received it intravenously.

``They are on the field very often 10 or 12 hours over each of two days,'' said O'Brien's coach, Rick Sloan. ``It's very easy for them to become dehydrated, and that starts affecting their performance drastically.''

But what if you're just an amateur marathoner like Howard Brown of Chatsworth, who simply wants to perform well at home?

Brown, too, has experienced firsthand the effects of a midsummer day's workout. Once, he was eight miles from home during a hot afternoon run when he felt too weak to continue. He walked to a nearby gas station and guzzled water from a hose before calling his wife to pick him up.

``I learned a long time ago to take water,'' Brown, 56, said. ``In the heat, I've learned to make adjustments, running more slowly or running shorter distances.''

Everyone - from the world's best athletes to the hordes of runners, in-line skaters and Little Leaguers who work out in the Valley each week - needs to take precautions against overheating when the temperature hovers near the century mark.

``The name of the game is prevention,'' said Dr. Luis Pacheco, director of predoctoral education at the University of Southern California School of Medicine. ``You need to drink beforehand and drink while you're doing the activity.''

In Atlanta, intravenous fluids will serve as just one way to battle the heat. Athletes from 70 countries training at 38 sites were supplied with 8 million ounces of sports drinks before the Games, and will receive another 4.1 million ounces of it on the field, officials say.

Even the spectators will have to take care not to get overheated.

``Some 250-pound guy who comes off the beer truck is going to be in as great a danger as the athletes,'' said Dr. Mark Adams, a U.S. Olympic Women's Soccer Team physician.

Just like the athletes, spectators who drink water have a better chance of withstanding the heat than those who down alcohol and caffeine, diuretics that cause water loss and frequent urination.

The body needs water at the cellular level for a host of metabolic processes, including kidney, gastrointestinal and brain functions, Pacheco said. Dehydration occurs when the body is not able to replenish fluids as quickly as they're lost. And if cells don't have enough water, they stop functioning.

Even mild dehydration can have significant effects, he said.

``Just 5 percent dehydration significantly impairs performance,'' Pacheco said. ``At 10 percent, it's dangerous. At 15 percent, you're talking about hospitalization.''

Warning signs of heat illness and dehydration include profuse sweating, rapid breathing and pulse, headache, dizziness and nausea.

A more serious heat illness is heatstroke, when the body's cooling mechanism shuts down and body temperature rises to as high as 106 degrees. Symptoms include hot, dry and red skin, confusion or unconsciousness.

A person who has heatstroke should be treated with cool compresses and liquids and taken to the hospital.

If you want to keep your body up to speed in the summer heat, follow these simple guidelines:

Drink more water. Sweating isn't pretty, but it's your body's most effective cooling mechanism. As perspiration evaporates, it removes body heat. In a one-hour workout, the body can lose up to a quart of water, or 2 pounds of body weight. The key to staying hydrated isn't waiting until you're thirsty, but drinking water before and during the workout.

Pacheco recommends drinking one or two 16-ounce glasses of water two hours before working out. Then about 30 minutes before starting to exercise, drink another 16 ounces of water.

Continue sipping water during the workout - about 4 ounces every 15 minutes should be sufficient.

Another option is sports drinks, which help replace electrolytes such as potassium and sodium that are lost during a workout. Sports drinks also contain carbohydrates that can be burned for quick energy. Try sports drinks for longer workouts, such as distance running or cycling.

A 6-ounce serving of grapefruit juice or a banana has more potassium than some sports drinks and can also replace electrolytes.

Avoid midday exercise. Southern Californians don't have to deal with the stifling humidity that Olympians will face in Atlanta, but we do have smog - air pollution that can cause respiratory problems and even lung disease.

That's why it's best to exercise in the morning or evening, or near the beach. Not only is the air cooler, but smog levels are lower.

``Smog is a real problem,'' Pacheco said. ``In the middle of the day, exercising near a congested area would be the worst place to do it.''

In any case, wear a hat, light-colored clothing and waterproof sunblock that has a sun protection factor of at least 15.

Get acclimated to warm temperatures. The body can adjust to weather conditions, but it takes time, Pacheco said.

To prepare for the Summer Games, for instance, most teams from around the world are training in Southeast cities to adjust to the warmer, more humid conditions. Runners from the University of California, Los Angeles, who are going to the Olympics will even train in sweats.

For non-Olympians, the idea is to start slow with a 10- or 20-minute walk, and build up to more vigorous exercise in warmer temperatures.

CAPTION(S):

Drawing, 2 Photos

Drawing: (Cover--Color) TOO HOT TO HANDLE

Wheth er they're in Atlanta or the Valley, people need to take precautions when working out in hot weather

Jim Thompson/Special to the Daily News

Photo: (1) ``In the heat, I've learned to make adjustments, running more slowly or running shorter distances,'' says amateur marathoner Howard Brown, 56, of Chatsworth.

Bob Halvorsen/Daily News

(2) During hot Olympic Trials in Georgia last month, Dan O'Brien and other decathletes couldn't drink water fast enough, so they received it intravenously.

Associated Press