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Eating For Endurance

It takes a lot of energy to run, cycle or ski long distances; to play three sets of tennis or a pickup game of basketball; or to walk for several hours. During intense exercise, your muscles draw sugar from your bloodstream at a rapid rate. Your liver can run out of its stored sugar and your blood sugar level can drop. You can markedly improve your performance in any of these events by eating shortly before your event begins, and by starting to eat and drink as soon as you start exercising.

The energy for your brain comes almost exclusively from the sugar in your bloodstream. When blood sugar levels drop, you feel tired and have difficulty coordinating your muscles. However, there is only enough sugar in your bloodstream to last three minutes at rest. To maintain blood sugar levels, your liver has to release sugar into your bloodstream. But there is only enough sugar in your liver to last around twelve hours at rest and far less than that when you exercise. When muscles run out of their stored sugar supply, it hurts to exercise and the muscles become difficult to control. Most people who exercise for more than an hour will improve their endurance if they start replenishing energy reserves as soon as they start to exercise.

Hunger during exercise is a very late sign of not getting enough calories. You can increase your endurance by starting to eat anything or to drink fluids that contain sugar as soon as you start to exercise. This will give you far greater endurance than waiting to take food after an hour of exercise or when you feel hungry.


Dear Dr. Mirkin: I ride a bike to work and don’t have any place to shower. How can I avoid offending my coworkers?

You don't have to smell bad just because you can't take a shower after a workout. Sweat doesn't smell when it first reaches your skin. The odor comes after bacteria on the skin's surface break down the fat and ferment the sugar in sweat to form chemicals that smell. It takes at least an hour for bacteria to produce an odor, and bacteria do this job best when the skin is wet.

Most of the glands in your skin secrete sweat that will not smell because it does not contain sugar of fat. Only the sweat glands around the bre*asts, gen*itals and armpits produce sweat that contains fat and sugar. You can prevent body odor by washing just these areas and then keeping them dry. Use antibacterial soap or towelettes ("baby wipes"), then apply powder to keep the skin dry, and a use deodorant.


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Dear Dr. Mirkin: Why would I have chest pain when I carry something heavy, but not at any other time?

You could have a condition called airport angina. It's named after a case report about a person who developed chest pain only when he ran to catch a plane while carrying a heavy suitcase.

The oxygen for your heart comes from blood vessels on its outside surface. The blood that is pumped inside of your heart does not supply significant amounts of oxygen or nutrition to your heart muscle. As long as your heart muscle can get all the oxygen that it needs, it doesn't hurt. When the blood vessels on the surface of your heart are partially blocked, your heart may be able to get all the oxygen that it needs for normal activities. However, when your heart needs to work extra hard, it may not be able to get enough oxygen so it starts to hurt.

When you walk carrying a heavy object, your arm muscles stay contracted and partially obstruct the flow of blood through their arteries. Your heart has to work harder to pump against this increased resistance. Narrowed heart arteries may not allow enough blood to flow through them and your heart will not get the extra oxygen that it needs, causing pain. Please check with your doctor.


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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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