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How Interval Workouts Improve Endurance

Most coaches and researchers are convinced that you have to do a series of short bursts of very fast speed training to improve long-term endurance, but they may not know why. The most offered explanation is that muscle fatigue caused by many hours of cycling is associated with a reduction in muscle fibers' ability to contract with force. A study from France shows that short bursts of very fast cycling improve endurance for cycling competitions that take many hours, because the stronger you are, the less of your maximal effort is needed to get the same pressure on the pedals (Medicine and Science in Sports and Exercise, January 2005.)

Muscles are made up of millions of individual fibers. Each fiber is a single muscular thread that functions independently. When you contract a muscle, you contract only a small percentage of these fibers at the same time. As each muscle fiber fatigues, you lose the ability to contract that fiber. When enough of these fibers stop contracting efficiently, you lose strength and your muscles feel tired. However, stronger fibers take longer to fatigue because they are being worked at a lower percentage of their capacity. So stronger muscles can be exercised for longer periods of time.

Making each muscle fiber stronger and bigger allows it to exert force for a longer period of time and therefore, increases endurance. The only way to make a muscle stronger is to exercise that muscle against progressively greater resistance, and that applies to each muscle fiber also. It is impossible to put great pressure on a muscle for a long time. When you do all-out fast bursts for a short time, you exert so much pressure that you have to back off after several seconds or a minute. All-out sprints for a short period followed by resting and then repeating the sprint is called interval training. It makes the entire muscle stronger and delays fatigue.

Athletes in all sports use long and short intervals. Short intervals take less than 30 seconds and because you do not build up significant amounts of lactic acid in that time, you can do hundreds of repeats in a single workout. Long intervals take two to three minutes and are very damaging to your muscles. Because you feel burning in your muscles and become very short of breath for a longer time, you can do only a few of these in a single workout. So athletes in all sports that require endurance do both long and short intervals to help them exercise longer.

Checked 10/19/17

May 11th, 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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