IOWA CITY, Iowa -- You may not be 20 anymore, but that doesn't mean the warranty on your joints has run out.

Osteoarthritis is not inevitable for people middle-aged and older who want to start playing sports or continue exercising regularly.

Moderate regular exercise in middle-aged and older people who are in good health and have no previous joint problems does not increase their risk of developing osteoarthritis, the most common form of arthritis, says a University of Iowa professor and UI football team physician.

"Joints aren't like the bearings on your car which wear out after a certain number of miles," says Joseph Buckwalter, UI professor of orthopaedic surgery. "The joint is a living structure; the cells are continually renewing themselves, and adapting to the load placed on them. Using the joints doesn't necessarily hurt them, in fact, the more you use them, the better off you may be."

This is the conclusion of Buckwalter's review of the often conflicting literature on the relationship between athletics and osteoarthritis, published in a current issue of The American Journal of Sports Medicine.

Osteoarthritis is a degenerative process of the joints where the articular cartilage is lost producing stiffness and joint pain. The condition is age related -- most people show signs of osteoarthritis by the time they are 40 or 45 -- but not caused by age. In fact, previous joint injury is a primary cause of the development of osteoarthritis, Buckwalter says.

Each bone of the joint is lined with a cartilage layer called articular cartilage. The articular cartilage contains fluid. When force, or stress, is put on the joint, through an activity such as jumping or running, the fluid moves to evenly distribute the impact. When the force is suddenly, repetitive and when there is torsional loading -- a twisting motion -- the articular cartilage and muscles don't have time to properly absorb the shock, increasing the likelihood of a joint injury. Football and soccer players and baseball pitchers and catchers are examples of athletes at high risk for damaging their joints. However, lifelong participation in sports and exercise don't necessarily result in osteoarthritis. Buckwalter points out that studies of long-distance runners show that runners don't have a higher incidence of osteoarthritis than non-runners.

"Physiological use of the body doesn't cause or accelerate degenerative joint disease," Buckwalter says. "In fact, it might be good for the joints."

Low-impact sports and exercise programs can improve strength and mobility in older people with normal muscle strength and normal joints, and in people with mild and moderate osteoarthritis, Buckwalter says. People who are at high risk for developing sports-related osteoarthritis are those who have: *Previous joint injury or surgery, *Muscle weakness, *Joint incongruity or dysplasia, *Unstable joints, *Sensory or motor defects, *Are overweight.

The risk of joint degeneration may be decreased by: *Selecting sports/exercise programs that have low impact and low torsional loading, *Use equipment and playing/running surfaces that decrease joint impact and torsional loading, *Maintaining and improving muscle strength, tone and conditioning *Decreasing body weight, *Alternating sports/exercise activities to decrease repetition of same patterns of joint loading and motion.

High-risk sports and activities include: Baseball/softball, basketball, volleyball, football, handball/racquetball, winter skiing and karate.

Moderate-risk sports include: Bowling, bicycling, rowing, ice skating, mountain climbing, ballet, canoeing and in-line skating.

Low-risk sports include: recreational swimming, golf, ballroom dancing and walking.

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