MONDAY, Nov. 30, 2009 (HealthDay News) -- If you're a middle-age weekend warrior who likes to hit the basketball court or hockey rink, take note: A new study suggests that high levels of physical activity boost the risk of internal knee damage that could lead to osteoarthritis.
The study found that the injuries occurred in middle-age people who showed no symptoms and had a healthy weight. They were more common and more severe in those who exercised more, although lower-impact activities such as swimming and cycling might actually be beneficial, according to the researchers.
The findings "speak to the importance of low-impact aerobic activity, especially in knees that are aging and may not be as resilient as they used to be," said Dr. Joseph Guettler, an orthopedic surgeon and sports medicine specialist at William Beaumont Hospital in Bingham Farms, Mich.
The problem is that bone and cartilage in the knee can develop cracks and fissures that worsen over time, "much as a pothole or crack in the pavement can become significant as cars keep driving over that area," said Guettler, who's familiar with the study findings but didn't take part in the research.
When people develop these sorts of problems, "we know that they're going to have an increased risk for arthritis later on in life," he said.
Osteoarthritis, the most common form of arthritis, develops when cartilage deteriorates in joints and causes bones to rub against each other.
In the study, radiologists examined MRI scans of the knees of 236 people who had enrolled in an osteoarthritis study. The participants, aged 45 to 55, included 136 women and 100 men. All participants completed questionnaires about their physical activity levels, which formed the basis for their assignment to high-, medium- or low-level activity groups.
The researchers then looked for links between levels of physical activity and the health of the participants' knees. The findings were to be presented Monday in Chicago at the annual meeting of the Radiological Society of North America.
Those who engaged in high levels of physical activity -- including such things as sports, exercise, yard work and housework -- had the highest levels of injuries. The injuries included fluid buildup in bone marrow and lesions in cartilage and ligaments.
"This study and previous studies by our group suggest that high-impact, weight-bearing physical activity, such as running and jumping, may be worse for cartilage health," the study's co-author, Dr. Christoph Stehling, a research fellow in the radiology and biomedical imaging department at the University of California, San Francisco, said in a news release. "Conversely, low-impact activities, such as swimming and cycling, may protect diseased cartilage and prevent healthy cartilage from developing disease."
Guettler, the Michigan surgeon, said that activities involving twisting, jumping and pivoting are especially hazardous. Don't overdo it when it comes to activities like basketball and soccer, he advised.
Instead, consider alternatives like walking, swimming, biking, cross-country skiing and training on elliptical machines, he said.
The researchers' next goal is to figure out whether low-impact and high-impact physical activity affect the progression of osteoarthritis differently, Stehling added.
The Arthritis Foundation has more on osteoarthritis.