People with damaged knee cartilage should give up running


November 02, 1993|By Dr. Gabe Mirkin | Dr. Gabe Mirkin,Contributing Writer United Features Syndicate

Most people who have injured the cartilage in their knees are better off not running or jumping for the rest of their lives, but rather relying on other low-impact exercises to maintain physical fitness.

At your knee, two bones meet and are held together by four bands, two on the outside and two on the inside. The ends of bones are soft, and they are protected by cartilage, which is a tough, thick white gristle. Cartilage can break when it is subjected to a strong force such as might happen when you are hit on the knee or unexpectedly step into a hole. Once broken, cartilage will never heal. Doctors can remove loose pieces, but they cannot make broken cartilage whole again.

A rise in the cartilage covering the upper bone in your knee fits into a depression in the cartilage covering the lower bone. When you break off some of the cartilage, the upper and lower cartilage does not fit together as well, so the joint loses stability and any hard force on the joint can knock off more cartilage. If you have knee cartilage damage and you continue to run and jump, you can expect more and more cartilage to be torn loose. Eventually, when all of the cartilage has been knocked loose, the exposed bone will hurt all the time and the knee may need to be replaced.

If you have damaged the cartilage in your knee, you are better off never running or jumping. Try riding a bicycle, swimming and walking only if it doesn't hurt when you do it. You should also be given exercises to strengthen the muscles that control your knees.

Q: Should I wear ankle weights while I jog? R. E., Duluth, Minn.

A: Wearing ankle weights when you run or walk increases your chances of injuring yourself. Every muscle in your body is balanced by other muscles that perform opposite functions. Muscles that bend your knee are opposed by those that straighten your knee, and muscles that raise your knee are opposed by those that lower it.

The quad muscles in the front of your upper leg raise your knee during running and walking. Your hamstrings in the back of your upper leg lower your knee. Opposing muscles develop strength proportional to the activity that uses them. Bicycle racers and hockey players have quad muscles and hamstrings that have approximately equal strength. Most runners and walkers have quad muscles in the front that are stronger than the hamstrings in the back. If their quads are more than twice as

strong as the hamstrings, they are more likely to tear the hamstrings.

Ankle weights add weight to your lower leg, causing your quad muscles in the front of your upper leg to work much harder to lift the heavier weight against gravity. This causes the quad muscles to become significantly stronger than the hamstrings, and it increases your chances of injuring both your quads and your hamstrings.

Your quads are more likely to be injured because they have to lift a much heavier weight when you raise your knees during running and walking. Your hamstrings are more likely to become injured because the quads pull with a greater force against them.

Q: I'm 58 and was recently diagnosed with diabetes. My doctor told me to start an exercise program. How can exercise help a diabetic? -- H. D., St. Louis

A: Most people who develop diabetes after the age of 50 can control their disease just by going on a low-fat diet, exercising and losing weight. Every cell in your body is like a balloon filled with fluid. On the surface of each cell's membranes are little hairlike projections called insulin receptors. Insulin cannot do its job of driving sugar from your bloodstream into cells until it first attaches to an insulin receptor. When your body can't make enough insulin, your blood sugar level rises and you develop diabetes, but the vast majority of people who develop diabetes after age 50 have enough insulin to control their blood sugar levels. Their disease occurs when their cells arenot able to respond to insulin because they don't have enough receptors.

The number of insulin receptors is determined by how much fat you have in your body and how much fat you eat. When cells are full of fat, they have fewer receptors. Emptying fat from cells markedly increases the number of insulin receptors on their surface.

You reduce the amount of fat in your body by eating less fat, losing weight and exercising. There's a good chance that when you exercise and lose weight, your blood sugar level will return to normal.

Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.

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