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Stretching Before Exercising Provides Only Flexibility

Whenever I see someone stretching before running, cycling, tennis, swimming, or any other sport, I worry that the person doesn't know much about training.

STRETCHING BEFORE EXERCISING WEAKENS MUSCLES: Two recent studies show that stretching before competition and training weakens muscles. Stretching prevents you from lifting your heaviest weights or running your fastest miles. It limits how high you can jump, and how fast you can run (The Journal of Strength and Conditioning Research, April 2013; The Scandinavian Journal of Medicine and Science in Sports, April 2013).

Stretching weakens muscles by almost 5.5 percent. The longer you hold the stretch, the more strength you lose. Holding a stretch for more than 90 seconds markedly reduces strength in that muscle.

Stretching reduces power -- how hard you can hit a baseball or tennis ball, or how fast you can swim, run or pedal. Stretching also does not prevent next-day muscle soreness, and it does not prevent injuries. On the other hand, warming up helps to prevent injuries and helps you to run faster and lift heavier.

HOW MUSCLES MOVE YOUR BODY: Every muscle in your body is made up of thousands of individual fibers. Each fiber is composed of sarcomeres; repeated similar blocks, lined end-to-end to form the rope-like fibers. Each sarcomere touches the sarcomere next to it at the Z line.sarcomereMuscles move your body by contracting, a shortening of each muscle fiber. Muscles do not shorten (contract) equally throughout their lengths. Muscles contract only at each of thousands of Z lines. It is the cumulative shortening of thousands of Z lines that shorten fibers to make muscles contract and move your body.

HOW STRETCHING SAPS STRENGTH: When you stretch a muscle, you pull on the muscle fibers and stretch apart each fiber at the thousands of Z lines. This damage occurs only at the Z lines throughout the length of the muscle fiber, to weaken the entire muscle.

PROLONGED STRETCHING LIMITS THE ABILITY OF MUSCLES TO STORE ENERGY: Muscles are like rubber bands. They stretch and contract with each muscle movement. This constant stretching and contracting stores energy. For example, when you run, you land on your foot and the muscle stops contracting suddenly. The force of your foot striking the ground is stored in your muscles and tendons and this energy is released immediately to drive you forward.

Your foot hits the ground with a force equal to three times your body weight when you run at a pace of six minutes per mile. Up to 70 percent of the force of your foot strike is stored in your Achilles and other tendons. This energy is released by your muscles and tendons to drive you forward for your next step. Stretching decreases the amount of energy you can store in muscles and tendons and therefore weakens you and you have less stored energy to drive you forward, so you have to slow down.

STRETCHING SAPS SPEED AND ENDURANCE: Elite college sprinters were timed in 20 meter sprints, with and without prior multiple 30-second stretches of their leg muscles. Both active and passive stretching slowed them down (Journal of Sports Science, May 2005).

STRETCHING DOES NOT PREVENT NEXT DAY MUSCLE SORENESS: A review of 12 studies published over the last 25 years shows that stretching does not prevent muscle soreness that occurs 8 to 24 hours after you exercise vigorously (The British Journal of Sports Medicine, December 2011; 45:15 1249-1250). Researchers in Australia reviewed five studies, involving 77 subjects, to show that stretching does not prevent next-day muscle soreness (British Medical Journal, December 2007; 325:468-70 and 451-2).

STRETCHING DOES NOT PREVENT INJURIES: A review of the scientific literature shows that there is no good evidence that stretching prevents sports injuries (Clinical Journal of Sports Medicine, March 2005). Muscles and tendons tear when the force applied to them is greater than their inherent strength, so anything that makes a muscle stronger helps to prevent injuries. Strengthening muscles helps prevent muscle and tendon tears, but stretching does not make muscles stronger. This review showed that stretching does not prevent shin splints, bone stress fractures, sprains, strains or other arm and leg injuries.


How Exercise Prevents and Treats Diabetes

A ground-breaking article from The Netherlands shows that lack of exercise is probably the most common cause of cell damage in diabetics today (Medicine and Science in Sports and Exercise. April, 2013). A high rise in blood sugar after meals, is a major cause of the horrendous cell damage in diabetics. Exercise can prevent blood sugar from rising too high after meals and destroying the cells in your body.

The authors studied sixty men with type II diabetes, which is caused by an inability to respond to insulin, not by lack of insulin. They showed that a single bout of exercise markedly lowered rises in blood sugar after meals throughout that day. The new information is that diabetics who thought they were controlled by having normal blood levels of HBA1C (the test that measures cell damage) were still getting considerable cell damage caused by higher-than-normal rises in blood sugar after meals.

The authors also showed that exercise markedly lowered these rises in blood sugar after meals. Other studies show that many people who are not diabetic, still have high rises in blood sugar levels after they eat, which can cause considerable cell damage even though they are not classified as diabetics.

WHAT CAUSES CELL DAMAGE IN DIABETICS? Every cell in your body is like a balloon full of fluid. Cell damage is caused by sugar sticking to the outer surface of a cell membrane. Once stuck on a cell, sugar can never get off. The sugar is converted by a series of chemical reactions from glucose to sorbitol, a sugar alcohol that destroys the cell. This is why diabetes can damage cells in every part of your body, which means that diabetes can cause blindness, deafness, dementia, heart attacks, strokes, impotence, kidney failure, liver failure, loss of feeling in your feet, and so forth.

HOW CAN YOU PREVENT HIGH RISES IN BLOOD SUGAR? Sugar sticks to cells when your blood sugar rises too high. The higher the rise in blood sugar, the more sugar sticks to cells. Blood sugar rises highest just after you eat.

You can keep blood sugar from rising too high by slowing the absorption of food from your gut, by avoiding foods that are known to cause a high rise in blood sugar, and by eating high- fiber foods that slow the absorption of other foods. You can also keep your blood sugar lower by contracting your muscles before and after you eat.

EXERCISE MAKES MUSCLES MORE SENSITIVE TO INSULIN AND ALLOWS MUSCLES TO TAKE UP SUGAR WITHOUT NEEDING INSULIN. Resting muscles draw virtually no sugar from your bloodstream. On the other hand, contracting muscles can draw sugar from the bloodstream without even needing insulin. Furthermore, exercise makes the muscle cells far more sensitive to insulin so that more sugar can be removed from the bloodstream with far less insulin.

YOU NEED TO EXERCISE EVERY DAY. The ability of muscles to remove sugar from the bloodstream is maximal during exercise. The more intensely you exercise, the greater the ability of muscles to remove sugar from the bloodstream. This effect is at its peak during exercise and for up to an hour after you finish exercising. It tapers off after that and is usually gone completely after about 17 hours.

WHEN IS THE BEST TIME TO EXERCISE? The best time to exercise is either just before or just after you eat. If you exercise just after you eat, your muscles can pull sugar from the bloodstream as fast is it is absorbed. If you eat right after you finish exercising, your muscles still have an extra hour to draw sugar maximally from the bloodstream.

• Eat lots of fruits and vegetables. They are full of fiber that delays absorption of sugar from other food sources.
• Avoid sugared drinks as the sugar in liquid form is absorbed faster than sugar in solid foods. You can take sugared drinks if you need extra energy during vigorous exercise, since contracting muscles will remove sugar rapidly from the bloodstream.
• Restrict all sugar-added foods.
• Avoid red meat. The saturated fats in red meat block insulin receptors to raise blood sugar levels.
• Avoid vitamin D deficiency. Lack of vitamin D blocks insulin receptors.


This week's medical history:
Ancel Keys, Cholesterol Debunker

For a complete list of my medical history biographies go to Histories and Mysteries


Recipe of the Week:

Fresh Fruit Bowl

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

April 7th, 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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