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Why You Need Interval Training for Both Speed and Endurance

To have great endurance for any sport, you have to do interval training: short bursts of moving almost as fast as you can, slowing down until you regain your breathe and then repeating these all-out efforts a number of times.

The old theory was that lactic acid makes the muscles more acidic which causes them to hurt and burn and interferes with their ability to contract, so you feel tired. George Brooks of the University of California/Berkeley has shown that lactic acid buildup in muscles does not make muscles tired and can make muscle contract more efficiently, which increases endurance. This research contradicts what many instructors teach in their exercise classes. When you exercise, your muscles burn sugar, protein and fat in the presence of oxygen to produce energy. If you exercise so intensely that you become very short of breath and your muscles can't get enough oxygen, lactic acid accumulates in your muscle fibers.

When you exercise, muscles need to get a lot of oxygen to turn all food sources into energy. In fact, the limiting factor to how fast you can move in sports competition is the time that it takes to move oxygen from the bloodstream in your lungs into your muscles. When you exercise so intensely that your muscles cannot get all the oxygen they need to turn sugar into energy, the series of chemical reactions slows down and lactic acid accumulates in muscles and spills over into the bloodstream.

Since lactic acid is an acid, the acidity causes muscles to burn and you have to slow down. However, as soon as you slow down enough to catch up on your oxygen debt, the lactic acid is immediately turned into more energy to power your muscles. In fact, lactic acid is a much better fuel for muscles than sugar, the second best source of energy. It is converted to energy with the lowest need for oxygen.

The major effect of regular training is to teach your muscles to use the lactic acid for energy before it accumulates in sufficient quantities to make muscles acidic to cause the painful burn and loss of strength and speed. You turn lactic acid into energy only in the mitochondria, small chambers inside muscle fibers. The more intensely you train, the greater your oxygen debt, so the larger your mitochondria become and the more mitochondria you produce in muscle cells. This helps you to turn lactic acid into energy for your muscles and requires the least amount of oxygen. Intense training is the best way to teach muscles to use lactic acid for energy. Using lactic acid efficiently for racing makes you faster and stronger and gives you greater endurance, even in competitions lasting many days.

The best way to grow new mitochondria, and to enlarge the ones that you have, is to do interval training. You move as fast as you can for a short period, become severely short of breath, slow down until you regain your breathing, and then go as fast as you can again. According to Dr. Brooks, "The intense exercise generates big lactate loads, and the body adapts by building up mitochondria to clear lactic acid quickly. If you use lactic acid up, it doesn't accumulate."

More than 20 years ago, Dr. Brooks showed that lactic acid moves out of muscle cells into the blood and enters all your organs including the liver and heart to give them an extraordinary source of energy that requires less oxygen than any other source. So the harder you exercise, the more efficiently your mitochondria turn lactic acid into energy requiring the least amount of oxygen.

Next week I will explain how to use the different types of interval training.


Dear Dr. Mirkin: Should I take prednisone for my rheumatoid arthritis?

Not unless other treatments do not help you feel better. A recent study from the University of Pisa in Italy showed that compared to rheumatoid arthritis patients not treated with prednisone, those treated with very low doses of prednisone had three times as many bone fractures, three times as frequent high blood pressure, and nine times as many heart attacks (Journal of Rheumatology, published online September 15, 2010). They took the extremely low dose of 4-6 mg/day of methylprednisolone, the amount that the human body normally produces each day.

Rheumatoid arthritis is thought to be an "auto-immune" disease. This means that the body's own white blood cells and antibodies that are supposed to kill invading germs, attack a person's own body to destroy the joints, muscles and tendons. Therefore, doctors give drugs to suppress a person's immunity. However, even the lowest doses of prednisone weaken bones, raise blood pressure and cause heart attacks.

The overactive immunity seen in rheumatoid arthritis patients would make you think that it is caused by an infection. However, researchers have failed to isolate any germ consistently in this disease, so they assume that it is caused by a person's own immunity attacking his own body, and therefore give drugs to suppress the overactive immunity. Drugs to suppress immunity can slow down joint destruction, but all have terrible side effects. At this time the best treatments we have are active exercise, medicines to relieve pain, and in extreme cases, drugs to suppress immunity.


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Dear Dr. Mirkin: Does having low testosterone cause heart attacks?

We don't know, but we do know that men with low testosterone levels are far more likely to suffer diabetes, heart attacks and premature death (Heart, published online October 20, 2010). We do not have studies to show that giving these men testosterone will prevent premature death or heart attacks. It could be that diabetes damages the testicles to cause low testosterone, and the diabetes also causes heart attacks and premature death. It could also be that low testosterone causes heart attacks.

Men with low testosterone levels should not take testosterone unless they suffer from lack of sexual desire or inability to perform sexually. We do not know if taking testosterone increases risk for heart attacks and prostate cancer.

Since low testosterone levels are linked with higher rates of heart attacks and diabetes, all men who have low testosterone should reduce their intake of red meat, sugared drinks and refined carbohydrates such as pasta and bakery products; increase their intake of fruits and vegetables; lose weight if overweight; control high blood pressure and high cholesterol; exercise (with doctor's permission); avoid smoke; take no more than two alcoholic drinks per day; and make sure that their vitamin D3 levels are above 75 nmol/L.


Recipe of the Week:

Wild Rice - Seafood Medley

You'll find lots of recipes and helpful tips in The Good Food Book - it's FREE

June 21st, 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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