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Hot Weather Makes Exercise Rough

July 26, 1998

WASHINGTON (AP) _ While Texas was baking in an intense heat wave, Harold Kohl was working up a sweat _ running in Houston at noon.

``I ran three miles around Rice Stadium,″ said Kohl, director of research at Baylor College of Medicine’s Sports Medicine Institute. ``It was HOT.″

Kohl conceded that Houston, benefiting from its proximity to the Gulf of Mexico, was only in the mid-to-high 90s _ not as hot as northern Texas, which was frying in the 17th day of 100-plus degree temperatures. ``I’m glad I’m not in Dallas,″ he said.

And Kohl was being cautious in his exercise _ as he and other experts advise, to avoid potentially fatal heat injuries.

``Drink water, drink water, drink more water,″ Kohl said. Before he ran, he drank 1.5 liters of water; afterward, he drank an additional liter, he said.

The water goes back out as sweat, which evaporates on the skin, cooling it and the hot blood that the body brings to vessels near the skin’s surface. And exercisers have to sweat a lot to keep their bodies in the normal temperature range. Above about 101-102 degrees, performance can fall _ and at 105-106, possibly fatal heat stroke can set in, Kohl said.

Exercisers must drink even when they are not thirsty, because the sensation of thirst lags the start of dehydration. Troops in the Gulf War had to force down water, under the watchful eyes of medical corpsmen, as a way to ward off heat stress.

``You should drink at least eight glasses of water under normal conditions,″ said Diane Guinan, a researcher at the Cooper Institute for Aerobics Research in Dallas. ``Add to that heat, and you need to add more water.″

Water will do fine, Kohl said. Electrolyte-laced sports drinks are only necessary for elite and ultra-endurance athletes who lose vast amounts of the minerals necessary to regulate heartbeat, among other functions, he said.

A person who drinks coffee, tea or caffeinated soda will need even more liquid, because caffeine is a diuretic, so it makes people want to excrete liquid, Guinan said.

Sweat is an early warning system for heat injury. Sweat that lingers on the skin is a sign of high humidity, and humidity retards the evaporative cooling needed to avoid trouble.

Sweat that turns clammy indicates the body’s heat-shedding mechanisms are breaking down, and it’s time to get cool fast. A cessation of sweat shows the system is in deep trouble _ that heat stroke is setting in, and medical attention is needed.

Sweat also can indicate how well the exerciser is adjusting to the heat, said Dr. Benjamin D. Levine, director of the Institute for Exercise and Environmental Medicine at Presbyterian Hospital in Dallas.

A person who is new to exercise in the heat will notice salt from the sweat is stinging the eyes and drying in rings on clothes, Levine said. This means the person is sweating too little, he said.

``After five or seven days, the sweat would not burn your eyes any more, and there are hardly any salt lines,″ Levine said. This indicates the body is adjusting to the heat by putting out more water _ effectively diluting the salt, he said.

It could take a week of increasing exercise to get the body used to workouts in hot weather, Levine said.

``Let’s say you run three miles in the morning in New Jersey and you move to Dallas,″ Levine said. ``The first day you run, you might get up earlier, you might run half as far and you might walk the other half. The next day you might wake up later, run three quarters and walk one quarter. The next day, you might run the whole thing, but have a longer warmup and a longer cooldown.″

The change in start times is to take advantage of cooler temperatures _ and lower pollution levels _ earlier in the day, Levine said.

Or exercisers can take the easy way out, and stay inside. The Cooper clinic complex checks temperature and humidity, then signals the safety of the day for outdoor exercise by flying colored flags.

``When you see a black flag, it’s pretty evident you should be exercising indoors,″ said Richard Little, fitness director at the Cooper Fitness Center. ``You have some diehards that prefer running outdoors, and still do so.″

Young people may not realize the risk, the experts say. Children’s heat-shedding systems are not as efficient as those of adults, so adults must monitor them _ and make sure they are drinking plenty of water, Kohl said.

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