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New Theory on Lactic Acid

A study from Australia shows that lactic acid buildup in muscles does not make muscles tired and may even make muscle contract more efficiently, which may increase your endurance (Science, August 26, 2004). This startling research contradicts what most instructors teach in their exercise classes. When you exercise, your muscles burn sugar, fat or protein 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.

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. This new research shows that rat’s muscles contact more efficiently when lactic acid accumulates in them. Electric currents cause muscles to contract. This electricity is generated by cell membranes causing potassium to move inside cells and chloride ions to stay outside. With vigorous exercise, potassium ions accumulate outside cells. As large amounts of potassium ions accumulate outside cells, electricity is not generated and the cells cannot contract. Another ion called chloride accumulates outside cells and prevents potassium from getting back inside cells. Lactic acid removes the chloride, so it is easier for potassium to get back inside cells. Therefore lactic acid increases the ratio of potassium inside cells to the amount outside, and this helps the muscle contract with more efficiency.

While this new concept of how muscles use lactic acid for energy is reasonable, it is not likely to change the way athletes train or the way exercisers become more fit. Healthy people are supposed to exercise vigorously and feel a burn in their muscles during exercise, which signifies buildup of lactic acid in muscles. They feel sore on the next day, go easy for as many days as it takes for muscles to feel fresh again, and then exercise intensely again.

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Dear Dr. Mirkin: How can I exercise with severe osteoarthritis in my knees?

When you complain that your knees hurt, your doctor tries to find a cause. If he can’t find a cause, he tells you that you have osteoarthritis. We don't have the foggiest idea what causes osteoarthritis and there is no effective treatment except pain medicines. The knee is two bones held together by four bands called ligaments, and the ends of bones are protected by thick gristle called cartilage. Osteoarthritis damages cartilage so it does not fit properly, making the knees unstable. Strengthening the muscles around the joint stabilizes the knee to allow less movement at the joint, increasing function and decreasing pain.

The most important part of a rehabilitation program for people with damaged knees is to strengthen the muscles of the upper leg that control the knee. However, pain and swelling often prevent people with severe knee arthritis from exercising their knees at all. Isometric strength training means to contract your muscles against an object that doesn't move, such as to push as hard as you can against a wall. If you place a resistance that does not move against the front of the ankles and contract your quad muscles in the front of your upper legs very hard, you can strengthen the quad muscles without moving your legs.

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Dear Dr. Mirkin: How many miles should I run each week to prepare for a marathon?

Many marathon runners think that they have to run 100 miles a week to compete successfully, but most will be able to run a marathon faster if they run fewer than 50 miles a week. Top marathon runners can run 100 miles a week and not be injured because of their superior genes. When most runners try to run 100 miles a week, they run too slowly in practice, and as a result, run too slowly in races.

To be able to compete successfully in any sport that requires speed, you have to train at a very fast pace. For runners, training at race pace or faster is far more important than how many miles they run. However, it takes time to recover after running fast, so most top runners are able to run very fast only once or twice a week. Most top marathon runners run very fast twice a week and long once a week. These three workouts form the basis for their training. All of the other workouts are done at a slower pace and should not be so fast or long that they leave you too tired to get through your three important training workouts.

A typical training schedule for a top marathon runner includes two workouts a day on weekdays and single workouts on weekends. They run very fast on Tuesday and Thursday afternoons and long on Sunday. They run at a slower pace on weekday mornings and Monday, Wednesday, Friday and Saturday afternoons.

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Recipe of the Week
Fruity Pebbles
Make a batch of my favorite “cookie” treat – No baking! Just try not to eat them all yourself.

More of Diana's healthful recipes

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June 27th, 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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