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Lactic Acid Increases Endurance

Lactic acid buildup in muscles does not make muscles tired and may even make muscle contract more efficiently, which may increase your endurance. This concept 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 muscles.

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. Now researchers have shown that 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 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 tell if I am pedaling my bicycle too fast?

Since fatigue during cycling comes from how much pressure you put on the pedals, not how fast you spin the pedals, you would think that the faster you spin the pedals, the longer you can ride and the greater your endurance. However, all cyclists learn sooner or later that they will reach a point when they spin too fast and the slow down and tire earlier.

A study from Purdue University in Indiana shows why you slow down when you pedal faster than your brain can coordinate your muscles (Medicine & Science in Sports & Exercise, April 2007). You get your maximal force during pedaling when the force of your foot is directed downward. When you pedal faster than is comfortable for you, the downward maximal force is applied later in the pedaling cycle so you never reach your maximum downward force of your feet on the pedals. Since you don't go down on your pedals with as much force, you lose force that starts you in your upward motion and have a weaker up stroke.

The key to pedaling efficiency is to pedal as fast as you can and still retain your maximum sustainable force on your pedals. Most people can tell when they are pedaling too fast because they start to feel uncoordinated when they raise their feet in the up stroke. Optimal cadence for competitive racers is between 90 and 105. Optimal cadence for most experienced riders is 80-85. Anyone pedaling at fewer than 70 revolutions per minute needs instruction and more practice.

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Dear Dr. Mirkin: Will exercise help or hurt my arthritis?

There is a direct relationship between the amount of physical activity and arthritis symptoms, according to a study published in Arthritis Research & Therapy (March 2007). In this study, 4,780 middle-aged women (48-55) and 3970 older women (72-79) were followed for three years. Those who were most active had the lowest incidence of joint pains. This does not mean that exercise prevents arthritis, but it does show a relationship between an active healthy lifestyle and absence of joint pain. Regular exercise strengthens muscles to stabilize and protect joints.

If you suffer from arthritis, check with your doctor. If he agrees, you should be in a regular exercise program. Activities that use smooth motions protect joints, while sports that involve jumping, running or other hard forces can cause damage. The safest exercises for a person with arthritis are swimming and using an stationary bicycle. Start out pedaling at a slow easy pace with very little pressure on the pedals and try to work up to an hour a day. If you feel pain as you exercise, stop for the day and try again on the next day.

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Recipe of the Week

Mexican Vegetable Stew

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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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