By Charlene Laino
WebMD Health News
Reviewed by Laura J. Martin, MD
Nov. 29, 2010 (Chicago) -- Light exercises such as walking and bowling and avoidance of knee-bending activities such as climbing and squatting may protect against osteoarthritis of the knee in at-risk people, researchers report.
On the flip side, high-impact sports such as running and skiing are associated with knee cartilage damage in people who are overweight, have had knee injuries or knee surgery, have a family history of osteoarthritis, or have other risk factors, according to a study presented here at the annual meeting of the Radiological Society of North America (RSNA).
Osteoarthritis is a degenerative joint disease that causes pain, swelling, and stiffness. According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, it's the most common form of arthritis, affecting an estimated 27 million Americans over the age of 25.
Analyzing Activity Levels
The new study involved 132 people at risk for knee osteoarthritis who were enrolled in the National Institutes of Health Osteoarthritis Initiative, as well as 33 people of similar ages and weight who were not at risk. Participants included 99 women and 66 men aged 45 to 55.
The researchers, led by Keegan Hovis, RN, of the University of California at San Francisco, separated participants into three exercise levels:
- Sedentary: watching TV, reading, or other sitting activities more than two hours a day, two or more days a week.
- Light exercisers: walking, playing darts, Frisbee or other light activities two or more hours a day, three or more days a week.
- Moderate to strenuous exercisers: running, cycling, or other moderate to strenuous sports more than an hour a day, three or more days a week.
Knee-bending activities such as climbing, kneeling, and lifting heavy objects were also analyzed.
Virtues of Light Exercise
Among people with osteoarthritis risk factors, MRI scans showed that light exercisers had the least amount of cartilage damage.
"It can be postulated that light exercise is protective against osteoarthritis" in these individuals, Hovis tells WebMD.
The scans also showed that women with osteoarthritis risk factors who fell into the moderate-to-strenuous exercise category had substantially more collagen degeneration in their knees than any other group.
Asked why men were not affected similarly, Hovis says that's unknown. "But women overall are at greater risk for osteoarthritis than men."
Among people who were not at risk for osteoarthritis, the exercise level did not affect cartilage degeneration.
However, frequent knee bending -- climbing 10 or more flights of stairs per day or kneeling for 30 or more minutes a day, for example -- was associated with more damaged cartilage in people with and without osteoarthritis risk factors.
Risks of Aggressive Exercise
Researcher Thomas M. Link, MD, chief of musculoskeletal imaging at the University of California, San Francisco, tells WebMD that cartilage doesn't regrow.
"We're not saying you shouldn't run or climb stairs. But you have to be extremely careful to protect your cartilage starting at a very early age," before you reach 40 or 50, he says.
The No. 1 thing you can do to protect your bone health is to shed excess pounds and maintain a healthy weight, says RSNA spokesman David Levin, MD, of Thomas Jefferson University Hospital in Philadelphia. He was not involved with the study.
Also, avoid exercising aggressively, Link says. "If you really injure a joint, you may initiate an osteoarthritis cascade that may be very difficult to treat."
Other modifiable risk factors include frequent knee bending and weak knee muscles, Hovis says.
Drawbacks of the study include the small number of people who were not at risk for osteoarthritis and the fact that only participants' current activity levels, not their lifelong history, were taken into account, she says.
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.
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