Children's exercise

Children need at least 90 minutes of exercise a day to avoid heart disease when they are older, according to a new study reported in Lancet (July 23, 2006). The old guidelines recommending 30 minutes of exercise three times a week, or even an hour a day do not appear to be adequate for preventing obesity and heart disease. Researchers used heart rate monitors to measure the activity of 1700 nine- to-fifteen-year-olds in Denmark, Estonia, and Portugal. They then calculated a heart-attack risk score consisting of blood pressure, cholesterol, insulin resistance, and skinfold thickness.

They compared physical activity from the heart rate monitors with the heart attack risk-factor score and found that the more active the child, the lower the heart attack risk score. Many children who exercised for 60 minutes a day were still overweight and had high heart attack risk scores. The authors suggest that the lack of regular physical activity is likely to mean that the children are spending too much time watching TV, playing video and computer games, and eating junk food. There is no reason to expect that the results would be different with American children. The current recommendation of at least an hour per day of moderate activity in children may not be sufficient for future heart health.

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Sports Drinks or Water?

Drinks that contain salt and sugar are better than just plain water during exercise, unless you are also eating foods. A study from the Medical College of Georgia shows that tennis players have lower body temperatures when they drink fluid with electrolytes and sugar, rather than just plain water (British Journal of Sports Medicine, May 2006). Higher body temperatures during exercise slow you down and tire you earlier.

More than 80 percent of the energy that supplies your muscles is lost as heat. Less than 20 percent drives your muscles. So during exercise, your heart has to cool your body by pumping hot blood from your muscles to your skin, as well as pumping oxygen-rich blood to your muscles. If you heart has difficulty serving both functions, it cannot pump enough hot blood from muscles and your temperature rises.

You do not have to take sports drinks to protect yourself from high body temperature. During exercise, you need energy, salt and water and your body doesn't care how it gets these nutrients. Eating any salted food with water or any beverage you like will supply your body as efficiently as sports drinks.

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Second wind

Second wind means that when you run very fast, you reach a point where you gasp for breath, slow down but keep on pushing and after a few seconds, you feel recovered and pick up the pace. Some people think that you just slow down and allow yourself enough time to recover from your oxygen debt, but research from the University of California in Berkeley may give another explanation.

When you run fast, your muscles use large amounts of oxygen to burn carbohydrate, fat and protein for energy. If you run so fast that your lungs cannot supply all the oxygen that you need, you develop an oxygen debt that causes lactic acid to accumulate in your muscles to make them burn, and you gasp for air. The muscle burning and shortness of breath caused by the accumulation of lactic acid forces you to slow down. This research shows that the lactic acid that accumulates in muscles when you run very fast actually is the first choice of fuel for your muscles when you are running so fast that you can't get all the oxygen that you need (American Journal of Physiology- Endocrinology and Metabolism, June 2006). So your muscles switch to burning more lactic acid for energy, you need less oxygen and then you pick up the pace. Of course when you keep on pushing the pace, you can again accumulate large amounts of lactic acid in muscles, which makes them burn and hurt again.

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Marathon training

Many runners have the mistaken impression that they have to run a lot of miles every week to be able to run fast in a marathon. Most will find that running too many miles slows them down. To run fast in races, you have to run very fast in practice. However, on the day after you run very fast, your muscles will feel sore. If you run fast while you are sore, you are likely to injure yourself and not be able to run at all. Take easy workouts until your muscles feel fresh again. Most competitive runners set up their programs so that they run fast on Tuesdays and Thursdays and longer on Sundays. The rest of the time they run slowly or not at all.

Before you increase the intensity of your running program or any other exercise, check with your doctor. Once you are in good shape, your goal on your fast days should be to run repeat intervals with short rests between each. For example, on Tuesdays try to run four half-mile repeats at a very fast pace with a quarter mile jog between each. If you can run a mile flat out in six minutes, you probably will try to run each half-mile repeat in about three minutes and 15 seconds. On Thursdays, try to run eight to 12 repeat quarter miles at close to the same pace of about 90 seconds each. On Sunday, try to run briskly for 90 minutes. The rest of the time, jog slowly, being careful not to run so much that it interferes with your two fast days and one long day each week.

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Exercise prolongs life

Dr. Todd Manini of the National Institute on Aging reports that older active people who walk, climb stairs, do household chores, or even wash windows are 69 percent less likely to die in a year, compared to people who are far less active (JAMA, June 2006). This study was far more dependable than previous studies because, instead of using a questionnaire, researchers measured how active a person was by measuring the metabolic end products of activity. They used a doubly-labeled water method that directly measures carbon dioxide production over an extended period, the most accurate estimate of energy expenditure.

If you are inactive, you should check with a cardiologist who will do a stress test. If you pass, you should start an exercise program. If you fail, you should work with your doctor to correct the problem and then start an exercise program.

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Weight lifting helps to prevent diabetes

One third of Americans will become diabetic because they eat too much and exercise too little. A study in Medicine and Science in Sports and Exercise (July 2006) shows that lifting weights can help to prevent and to treat diabetes.

Extra fat prevents your body from responding normally to insulin. Before insulin can do its job of driving sugar from the bloodstream into cells, it must first attach to little hooks on cell membranes called insulin receptors. Having extra fat in cells turns these receptors inward, making it far more difficult for insulin to attach to the receptors. This prevents insulin from doing its job of lowering blood sugar levels, even though your body is making plenty of insulin. That’s why anything that makes you fat increases your risk for diabetes. Doctors can measure how cells respond to insulin with a sugar tolerance test.

In this study, adolescent boys were given a program of lifting heavy weights twice a week. After only 16 weeks, their muscles were larger and they lost fat. Sugar tolerance tests showed that the ability of their bodies to clear a load of sugar from their blood streams improved dramatically. This means that a regular weight lifting program decreases insulin resistance and thus reduces risk for becoming diabetic.

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Dizziness on changing position

Athletes and other very fit people may feel dizzy when they rise from lying to standing because of their slow pulse rates. Exercise makes your heart stronger so it can pump more blood with each beat and it doesn't have to beat as often. A slow pulse rate can be good. Since your heart doesn't beat as often, it has more time to rest between beats. Like a low-mileage used car, perhaps this will mean it takes longer to wear out. But a slow heart rate can make you dizzy when you change position.

When you raise yourself from lying to sitting, or from sitting to standing, the force of gravity pulls blood down from your brain towards your feet and your blood can't get back to your brain until your next heart beat. If you have a pulse rate of only 50 beats a minute, it will take more than a second between beats. That can be enough time for your brain to suffer briefly from a lack of oxygen, so you feel dizzy. You can even pass out while you wait for your next heartbeat to come along and pump blood back up to your brain.

Dizziness can also be a sign of an irregular heartbeat or blocked arteries leading to your brain, so people who feel dizzy when they get up should check with their doctors. If they are athletes, chances are that they only have a strong athletic heart with a slow rate, and all they need to do is remember to get up slowly.

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