Middle-aged and older adults who exercise may not be reducing their risk of knee arthritis, but they aren’t increasing the risk either, research published Wednesday suggests.

The question of whether exercise helps or harms older knees has lacked a straightforward answer. Some studies have suggested, for instance, that exercise might help prevent knee osteoarthritis (OA) by increasing the thickness of the cartilage cushioning the joint.

On the other hand, some studies have found that older adults who exercise have a higher rate of knee OA. In particular, there’s some concern that overweight adults, who already have extra stress on the knee joints, might further raise their odds of arthritis through exercise.

In the new study, researchers followed the rate of knee arthritis development among nearly 1,300 men and women for about nine years; the average subject age at the beginning of the study was 53 years.

Overall, participants who regularly walked, jogged or otherwise worked up a sweat were at neither greater nor lower risk of developing knee OA, Dr. David T. Felson, of the Boston University School of Medicine, and associates report.

This was true regardless of body weight and type of exercise, according to the report in the journal Arthritis & Rheumatism.

Even though exercise didn’t ward off knee arthritis, the findings can be seen as good news, Felson, the study’s lead author, told Reuters Health. Moderate, recreational exercise does at least appear safe for older knees.

A separate study published in the same journal issue suggests that, similarly, exercise may not affect the progression of knee OA after it’s diagnosed.

In a review of 36 previous studies, researchers in the Netherlands found that, taken together, the research showed no consistent evidence that exercise altered the progression of knee OA.

The review also found that a host of other factors were similarly unrelated to OA progression - including the severity of knee pain, the severity of the joint damage on X-rays, thigh muscle strength and history of knee injury.

Regarding the factors that do boost the risk of developing knee OA, Felson said that being overweight or obese “clearly increases” middle-age and older adults’ risk.

Recent research also suggests that a number of more subtle differences among people influence the odds of knee OA, according to Dr. Marian A. Minor, a professor of physical therapy at the University of Missouri in Columbia.

Among these are leg alignment - being “bow-legged” or “knock-kneed;” the knee joint’s ability to sense position and speed of motion; and job activities like squatting and heavy lifting, explained Minor, who wrote an accompanying editorial.

For now, she told Reuters Health, it seems that moderate activities like walking and jogging are not risk factors. “It’s fairly safe to say now that moderate daily physical activity does not increase risk.”

SOURCE: Arthritis & Rheumatism, February 15, 2007.