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Muscle Fatigue in Endurance Events Is Caused by Muscle Damage

When you exercise for a long time, your muscles start to burn and feel sore, which forces you to slow down. You call this fatigue and tiredness, but a recent study from Japan shows that muscle fatigue is caused by damage to the muscle itself (Medicine & Science in Sports & Exercise, July 2005). This also explains why exercising long and hard enough to feel the burn for an extended period leaves your muscles sore for one or more days afterwards. Athletes call this Delayed-Onset Muscle Soreness (DOMS) and they learn that they have to have this next-day soreness to improve for competition.

Running is much more fatiguing than cycling. When you run, your heel hits the ground and stops your leg from moving. This sudden stopping with each foot strike stretches your contracting muscles and tears them to cause a lot of muscle damage. It’s called eccentric contractions of muscle and occurs with far less force in cycling. You pedal with a smooth rotary motion and do not stop suddenly. The eccentric contractions during running cause a high degree of muscle injuries, limit how far person can run fast, and require far more rest days or easy days than cyclists use in their training programs.

Since muscle fatigue during endurance competitions is caused by muscle damage, anything that strengthens muscles will improve performance in endurance events. The only way to make a muscle stronger is to damage the muscle with hard exercise, feel sore on the next day, exercise more easily on as many days as it takes for the soreness to go away, and then exercise vigorously again. Athletes in competitive sports must exercise at a reduced intensity on the days that their muscles feel sore. This makes muscles more fibrous and resistant to injury so that muscles can withstand greater forces when athletes exercise on their hard days.


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Dear Dr. Mirkin: Are statin drugs the best way to lower cholesterol?

The Treatment to New Targets (TNT) study reported at the 2005 meeting of the American College of Cardiology showed that very high doses of 80 mg per day of Lipitor lower cholesterol far better than lower doses, and reduce the rate of heart attacks and strokes by 29 percent. At the 2006 meeting, the Asteroid study showed that taking 40mg per day of Crestar for one year removed plaques from arteries. These studies show that your doctor should try to lower blood levels of the bad LDL cholesterol as much as possible, probably to below 75. Statin drugs such as Lipitor usually don’t cause many serious side effects, but they can cause muscle pains, particularly in heavy exercisers.

On the basis of this latest research, doctors are encouraged to treat people at high risk for heart attacks with diet and high doses of statin drugs. People with high blood pressure, high cholesterol, or diabetes are at the highest risk. All people at increased risk for heart attacks should restrict saturated and partially hydrogenated fats and refined carbohydrates, and base their diet on plants: fruits, vegetables, whole grains, beans and other seeds, whether or not you take drugs.


Dear Dr. Mirkin: Does marriage affect a man’s testosterone?

Apparently it does; married men with and without children have significantly lower testosterone levels than unmarried ones and the more time a man spends with his wife and children, the lower his testosterone level (Psychoneuroendocrinology, Volume 29, 2004). A man's testosterone levels drop significantly when he holds an infant. Testosterone begins to decline shortly after marriage, but surges upward when unions end in divorce. High levels of testosterone cause men to fight and mate. Lower levels of testosterone may keep men home to care for their wives and children. Testosterone levels can be measured in saliva. A more serious cause of low testosterone


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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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