Science from our Sisters

Exercise Habits Do Not Affect Development of Knee OA in Older Adults

Could exercise, due to an increased loading on the cartilage, increase the odds of developing knee osteoarthritis (OA)? Happily, the answer appears to be no. Moderate physical exercise has no effect—positive or negative—on the development of knee OA, according to a study published in Arthritis Care & Research (2007;57:6-12).

Previous research had not answered the question definitively. Lead author David Felson, MD, MPH, professor of medicine at Boston, says older studies used small pools of subjects and didn’t do long-term follow-up measurements. “It takes a long time to develop osteoarthritis, so following people for just a couple of years, especially with a smaller sample, just isn’t enough,” he explains. This new study lasted more than nine years, using more than 1,200 subjects from the Framingham Heart Study database.

Starting in 1993, Felson’s team took baseline measurements of 1,705 patients, mostly middle-aged subjects from Framingham’s offspring cohort who did not have any signs of OA. Each subject had weight-bearing, fully extended x-rays taken of both knees. They also answered a series of detailed questions about their history of knee pain symptoms and regular exercise habits.

Between 2002 and 2005, Felson’s team sought out the initial subject pool to repeat the measurements. About 75% (1,279 subjects) went through the second examination, which followed the same X-ray protocol as the baseline examination.

Blinded to patient details, two independent readers compared each subject’s baseline and follow-up X-rays. They gave each a Kellgren and Lawrence (K/L) grade—a quantitative determination of the incidence of OA. If the two readers disagreed on K/L grades, a third independent reader was asked to adjudicate.

Subjects were divided into three groups based on exercise habits reported during the baseline examination: no walking for exercise, walking less than six miles per week, and walking more than six miles per week. Slightly more than 9% of subjects developed incident OA, with no significant difference between exercise groups.

Overweight subjects were significantly more likely to get OA (13.7% versus 5.9%, respectively); however, overweight subjects who exercised were no different than overweight subjects who did not exercise. For both normal overweight subjects, exercise did not contribute to an increased risk of OA.

Though this study showed that moderate exercise doesn’t increase the risk of OA, Dr. Felson says older patients should probably avoid more intense exercise. “We studied mostly recreational walking… . We’re not saying anything about jogging or running—I’m not sure that’s going to be safe.”