"There really was no difference between those who exercised and those who didn't in terms of getting knee osteoarthritis," says researcher David T. Felson, MD, MPH, professor of medicine and epidemiology at Boston University.
Over the nine-year study period, exercise didn't raise or lower the risk of getting knee arthritis, he says.
His study, as well as another review study and an editorial, are published online and in the Feb. 15 issue of Arthritis & Rheumatism.
Felson and his colleagues questioned more than 1,200 men and women who participated in the Framingham Offspring cohort, including children of participants in the original Framingham Study, which has looked at cardiovascular disease risks since 1948.
At the beginning of the arthritis study, the average age of participants was 53. In 1993-1994, Felson's team gave them knee X-rays and questioned them about any pain, aching, or stiffness in the knees. Most subjects reported that they walked for exercise; only 68 jogged or ran.
Felson divided participants into three groups: sedentary, those who walked six or more miles weekly, and those who walked less than six miles a week for exercise.
The researchers began to conduct follow-up exams in 2002, taking additional knee X-rays and asking again about knee symptoms. Weight was recorded at the start and at the final follow-up, when specialists read the X-rays to look for evidence of arthritis.
On average, the participants' body mass index or BMI was 27.4; below 25 down to 18.5 is deemed normal weight; 25 to 29.9 is considered overweight.
Among those who did no exercise, 7.5% got knee arthritis with symptoms over the course of the study; 4.9% of those who walked less than 6 miles a week also got knee arthritis with symptoms, along with 6.4% of those who walked 6 or more miles a week. To a scientist, Felson says, those differences are not significant.
"I personally had thought there would be some risk," Felson says. "A lot of these people were very overweight." Obesity is a risk factor for getting knee osteoarthritis, other research has shown.
Arthritis Risk and Healthy Knees
"This is another study that furthers our belief that moderate physical activity does not increase the risk of knee osteoarthritis," says Marian A. Minor, PhD, professor and chairwoman of physical therapy at the University of Missouri at Columbia, who wrote an editorial to accompany the study.
She cautions, however, that "the study results apply to healthy knees."
In the same issue, a review of 37 published studies, conducted by researchers from Erasmus Medical Center in Rotterdam, Netherlands, showed regular sports activities are not related to getting arthritis in the knee.
They didn't find a link, either, between knee pain, knee injury, and later arthritis in the joint.
An Exercise Physiologist's View
The research showing no increased risk of getting knee arthritis among older exercisers rings true with his clinical experience, says Richard T. Cotton, an exercise physiologist and wellness coach who serves as a spokesman for the American Council on Exercise.
"People who have made it to their 50s without knee problems tend to be OK,'' he says.
To minimize the risk of problems, however, Cotton tells exercisers to increase their exercise distance very gradually, then increase speed, rather than both at once.
Good workout shoes matched to your activity -- walking, jogging, aerobics, or hiking -- are crucial, he says. "Don't wear them to mow the lawn or go to the mall," he says. Save them for the exercise activity.
And replace them every 3-6 months if you are exercising regularly, he says.
SOURCES: David T. Felson, MD, MPH, professor of medicine and epidemiology, Boston University. Felson, D.T. Arthritis & Rheumatism, Feb. 15, 2007; vol 57: pp 6-12. Minor M. Arthritis & Rheumatism, Feb. 15, 2007; vol 57: pp 1-2. Belo, J. Arthritis & Rheumatism, Feb. 15, 2007; vol 57: pp 13-26. Richard Cotton, MA, exercise physiologist; wellness coach; spokesman, American Council on Exercise, San Diego. Marian Minor, PhD, professor and chairwoman of physical therapy, University of Missouri, Columbia.
By Kathleen Doheny
Reviewed by Louise Chang