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Why You Should Cool Down

At the end of a marathon, a runner sprints over the finish line, falls down and lies unconscious for a short time. What's the most likely cause? The possibilities include dehydration, hyponatremia (excessive fluid intake with too little salt in the blood), heat stroke, drunkenness, a heart attack or stroke. Usually it is none of these. Almost all athletes who collapse after finishing a marathon suffer from postural hypotension: lack of blood flow to the brain because blood drops from the brain to the legs. Treatment is to lie the person on his back, raise his feet high over his head and wait for him to revive. If he or she is not alert within seconds, you should consider the more serious causes of unconsciousness and get medical help immediately.

When you run, your heart pumps blood through your body, but it gets lots of help from your legs. When your leg muscles contract, they squeeze veins near them to push blood toward your heart. When your leg muscles relax, the veins near them fill with blood. This alternate contracting and relaxing of your leg muscles serves as a second heart. When you sprint toward the finish line, your leg muscles increase their pumping of blood. If you stop suddenly, the leg muscles top pumping and blood pools in your legs, your brain doesn't get enough oxygen, and you pass out.

This is the reason you should always cool down after vigorous exercise. If you slow down gradually, your leg muscles stop pumping gradually and you heart has time to pick up its share of the workload. Many people believe that cooling down helps to prevent muscle soreness by clearing lactic acid from muscles, but there is no evidence to support this theory. Muscle soreness after exercise is caused by small tears in the muscle fibers, not by accumulated lactic acid. Plan to cool down just to prevent dizziness or fainting.


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Dear Dr. Mirkin: Is there any good evidence that exercise helps to prevent memory loss? Dementia with aging is associated with every risk factor for heart attacks: smoking, overweight, lack of exercise, high blood pressure and cholesterol, abdominal obesity, diabetes, kidney damage, eating too much saturated fat, refined carbohydrates and calories, not eating enough vegetables, and so forth. A study from the University of Edinburgh in Scotland shows that if you don't want to lose your mental function with aging, you had better start and stay on a vigorous exercise program (Neurology, October 2006).

Four hundred and sixty survivors of the Scottish Mental Survey of 1932 were tested on the same general memory tests at age 11 and again at age 79. They also were tested at age 79 for their level of physical fitness by having tests for grip strength, 6- meter walk time, and lung function. Those who had the highest scores for physical fitness also had the highest scores for mental function. They also found that those with the highest IQ at age 11 had the best lung functions at age 79, which may mean that intelligent people are more likely to stay in shape. This study adds to the evidence that physical exercise protects your brain. More


Dear Dr. Mirkin: I read an article saying that leucine increases endurance; is it safe and effective? A study from Australia showed that leucine helps athletes exercise longer (European Journal of Applied Physiology, August 2006), so now athletes are lining up to waste their money on supplements that are no more effective than any other source of sugar.

Leucine is a branched chain amino acid that the liver readily converts to sugar. Your body needs extra sugar during endurance exercise, and it doesn't care where it gets it. Your brain gets more than 95 percent of its energy from sugar in your bloodstream. It cannot store extra fuel in its cells. However, there is only enough sugar in your bloodstream to last three minutes. To prevent blood-sugar levels from dropping, your liver constantly releases sugar from its cells into your bloodstream. There is only enough sugar in your liver to last up to 12 hours at rest, and you run out of liver sugar much faster than that when you exercise.

Your liver then makes sugar out of certain protein building blocks called branched chain amino acids in a process called gluconeogenesis. So taking leucine, a branched chain amino acid, helps to maintain blood sugar levels, but so will eating any source of carbohydrates. Athletes buy special concentrated sugar gels, mineral-sugar drinks, and all sorts of expensive exercise foods. None are any more effective in prolonging endurance than ordinary food sources of carbohydrates such as a soda, an orange or banana, a peanut butter and jelly sandwich, a bagel, cookies or whatever you like.


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June 26th, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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