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How dry I am....

You may have heard about Abduul Reed. In September of 1988, the Arizona teen stepped onto the field for his first day of high school football practice. For several hours, Reed and his teammates ran through a variety of grueling drills in the 40 [degrees] C heat. Shortly after the practice ended, Reed collapsed and died.

The cause, doctors said, was sudden heart failure brought on by overexertion, overheating, and dehydration - a water shortage that results when the body loses more water than it takes in. In effect, Reed had sweat to death.


Death by sweating? It's hard to imagine. After all, everybody sweats. It's the body's way of keeping cool. And it's usually no big deal to replenish the water you lose to perspiration. You sweat, you get thirsty, you drink a glass of water. No problem.

But when you push your body to the limit like Reed did, you can lose as much as 3.5 liters of sweat every hour. When that much liquid leaves your body, you're in the dehydration danger zone. After all, you're practically made of water. All your organs need the stuff to run properly.

It doesn't matter what sport you play, or what the weather is like. Strenuous exercise of any type-football, basketball, skiing, whatever-will sap you of liquid in a hurry. To make matters worse, you may not even feel thirsty until you've already lost a considerable amount of water. If you do feel excessive thirst - or cramps or clammy skin - call it a day. These are signs that your body needs liquid fast.

So what should you drink? Several companies have come up with specially formulated "sports drinks." These beverages, their makers explain, are isotonic - they have the same concentration of water molecules and dissolved salts as the fluid in your cells (iso- means "same" or "equal"). So, the ads claim, they're ideal for replacing the water and minerals you lose when you sweat.

That's nonsense, according to most doctors and nutritionists. Sports drinks, they say, do little to replenish the liquid your body loses during a heavy-duty workout. You can figure out why for yourself if you look at how water molecules move into and out of cells (see diagram).


Keep in mind that cells "seek" balance between their internal and external environments. In other words, they "like" to have the same concentration of water and dissolved substances on both sides of their cell membranes. When the concentrations are uneven, water flows through the membrane to balance things out. This movement of water across a membrane to equalize concentrations is called osmosis.

What happens when you chug down a sports drink after, say, playing a couple hours of tennis? Think about it. Your cells are probably not all that dehydrated. They still have their normal concentration of dissolved salts and sugars. Bathe them in a sports drink with that same concentration, and basically nothing happens. There's no reason for water in the drink to move into your cells. No harm done, but no particular benefit either.

If you are dangerously dehydrated, though, experts say you should avoid sports drinks. The reason: They are loaded with sugar. Sportsdrink makers say it's there to give you a quick "energy boost." But in fact, the sugar drags you down, because your digestive system processes sugar slowly. That means the water in sports drinks takes a long time to get to where it's desperately needed - your thirsty cells.

Plain water, by contrast, passes through your system rather quickly. And water is hypotonic - it has a lower concentration of dissolved substances than the fluid in your cells (hypo- means "less than"). That means the water will rush into your cells. No surprise, then, that scientists say plain old [H.sub.2]O is the best drink for thirsty athletes.

Of course, many people think sports drink taste better. "If you prefer the sweetness of Gatorade to plain water," says Dr. Michael A. Nagel, "at least dilute the drink with an equal amount of water." That will cut down the concentration of sugar and salts and get the water that is in the sports drink to your ceus faster.




You can exercise to your heart's content without drying out your insides if you . . .

* Drink plenty of water before you start exercising and train yourself to take frequent water breaks throughout your workout

* Avoid exercising at the hottest time of day

* Stay away from drinks that contain alcohol or caffeine - both dehydrate you

* Give your body time to adjust to the physical strain of exercise by starting slowly and gradually increasing the intensity and duration of your workouts
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Title Annotation:replacing body fluids
Author:Plaut, Josh
Publication:Science World
Date:Dec 4, 1992
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