ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Tuesday, June 18, 1996 TAG: 9606180037
SECTION: EXTRA PAGE: 1 EDITION: METRO
COLUMN: PERSONAL HEALTH
SOURCE: JANE BRODY
When Alberto Salazar won the Boston Marathon in 1982, he fell into a coma right after crossing the finish line. Salazar sweats heavily, and he became so hot and dehydrated during the race that his organ systems were near collapse. Dr. William Castelli and a police officer saved his life by squeezing more than three quarts of replacement fluids into his veins.
Few recreational athletes push themselves to such limits. But even those who, say, play an hour and a half of singles tennis or run a 10-K or cycle 20 miles, especially on a hot day, often risk the effects of dehydration.
For example, a 15-year-old boy from Utah recently died from the heat after he and his friends ran out of water while hiking in the Grand Canyon. But even an ordinary fitness walker can lose large amounts of water in hot weather or on a challenging course.
Unfortunately, thirst is an imprecise signal that often fails to kick in until the body is approaching a danger point. You may have lost two quarts of water - four pounds - before thirst prompts you to start drinking.
Experts in exercise physiology say that few athletes, whether amateurs, elites or professionals, drink enough fluids before and during their activities to counter the ill effects on performance and well-being that can result from below-normal amounts of body water.
People who sweat heavily are especially at risk and are least likely to drink enough, said Dr. Michael N. Sawka, an expert in thermal physiology at the U.S. Army Research Institute for Environmental Medicine in Natick, Mass.
Older people who are physically active are also at greater than average risk because thirst sensation, sweat production and ability to concentrate urine decline with age. It is especially dangerous to exercise in clothing that does not breathe. Wearing plasticized garments to foster sweating does not increase the loss of body fat and can endanger health.
Need for water
Sawka, who spoke at a recent National Institutes of Health workshop on dietary needs of physically active people, said water loss that resulted in as little as a 1 percent drop in body weight (a mere 1.5 pounds for a 150-pound person) could raise body temperature because dehydration causes the body's main cooling mechanisms - blood flow to the skin and sweating - to become less efficient.
As body temperature rises, the risk of heat exhaustion and heat stroke, which can be fatal, rises too. The heart beats faster (an indication of cardiovascular strain), muscles fatigue sooner and exercise performance declines by 20 percent to 50 percent.
As the American College of Sports Medicine put it in a recent position statement on exercise and fluid replacement, ``Inadequate water intake can lead to premature exhaustion.''
Instead of feeling relaxed and invigorated after a workout, the dehydrated exerciser is likely to feel stressed out, unduly fatigued and lethargic, perhaps even headachy, dizzy and nauseated and may not feel much better the next day either.
Dr. Edward F. Coyle, director of the Human Performance Laboratory at the University of Texas, said cyclists rarely drink enough while riding. Yet few realize the decline in performance that results. So he placed a group of cyclists in a heat chamber to dehydrate them and, before and after, had them peddle a bicycle ergometer that measured speed and heart rate.
``When they saw how much dehydration caused their heart rates to rise and slowed them down, it turned them into true believers about drinking more,'' the professor of kinesiology said.
The college's statement put it this way: ``During exercise, humans do not typically drink as much water as they sweat and, at best, voluntary drinking only replaces about two-thirds of the body water lost as sweat. It is common for individuals to dehydrate by 2 percent to 6 percent of their body weight during exercise in the heat despite the availability of adequate amounts of fluid.''
Becoming acclimated to the heat does not help the body conserve water. In fact, Sawka said, because acclimatized individuals are better able to sweat, they actually need more water, not less, to avoid dehydration.
How much water?
The smart athlete or exerciser will always start out well-hydrated. Ideally, two hours before an activity, you should drink about 16 ounces of water. Any excess will be lost through urination before the event. But if you do not have to urinate within an hour, drink another 8 ounces.
If you cannot drink water two hours in advance, drink 8 ounces to 16 ounces before starting your activity. In either case, continue to drink water throughout the activity, consuming 6 to 12 ounces every 15 to 20 minutes, especially when exercising in the heat. To foster maximum consumption and rapid absorption into the blood, the water should be cool - from 40 to 50 degrees Fahrenheit - but not ice-cold.
To be sure you have consumed enough water, weigh yourself before and after the activity, preferably unclothed, since sweaty clothes weigh more than dry ones. For each one-pound deficit in body weight, you will need to drink a pint (two cups) of water to replace the water you lost as sweat. Remember, you cannot rely on thirst to tell you how dried out you are.
Of course, in addition to water, sweat contains essential minerals: sodium, chloride ion and potassium. But their concentration in sweat is much lower than in blood, so in sweating you lose proportionately more water than minerals.
Ordinarily, these minerals are readily replenished through foods consumed as snacks and meals. Special sports drinks are not recommended unless you engage in intense exercise for more than an hour. The main advantage of such drinks for the average active person is that their flavor and sweetness encourages greater fluid consumption.
While a small amount of caffeine (the amount in a Diet Coke, for example) may foster muscle action, Sawka says that those who drink a lot of beverages containing caffeine before exercising could start out dehydrated, since caffeine is a diuretic.
Alcohol is dehydrating too, and anyone who has more than one drink the night before a morning activity should drink two cups of water before bed and another two on arising.
The statement from the college of sports medicine points out that small amounts of sugar can enhance the absorption of water and, for prolonged, intense activities, delay muscle fatigue by maintaining normal levels of glucose in the blood.
But a drink with too much sugar - the amount, say, in an ordinary soft drink or juice - has the opposite effect. It draws water into the gut from the blood, which aggravates dehydration and may cause bloating and cramps. Also, drinks that contain fructose as their main sugar are too slowly converted to glucose to be useful in delaying fatigue.
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