Nov. 30, 2009 (Chicago) -- Weekend warriors, take note: Too much exercise may place you at risk for arthritis.
A new study shows that middle-aged men and women who engage in high levels of physical activity -- at home and at work as well as at the gym -- may be unwittingly damaging their knees and increasing their risk for osteoarthritis.
The study involved men and women of healthy weight, without pain or other symptoms. Knee injuries were more common and more severe among those who engaged in the highest levels of physical activity, says Christoph Stehling, MD, of the University of California, San Francisco, and the University of Muenster, in Germany.
The findings were presented at the annual meeting of the Radiological Society of North America (RSNA).
High-Impact Exercises Worse for Knee Health
Doctors aren't sure that painless cartilage and bone damage can lead to osteoarthritis, but they think they do, says RSNA spokesman Joseph Tashjian, MD, president of St. Paul Radiology, in Minnesota.
What is known, he tells WebMD, is that high-impact, weight-bearing activities such as running and jumping are worse for knee health and carry a greater risk of injury over time.
"Conversely, low-impact activities, such as swimming and cycling, may protect diseased cartilage and prevent healthy cartilage from developing disease," Stehling says.
Osteoarthritis, in which the wear and tear of joints over the years leads to the breakdown of cartilage, affects about 27 million Americans, according to the CDC.
More Activity, More Knee Damage
The study involved 136 women and 100 men, ages 45 to 55, within a healthy weight range. The participants were separated into low-, middle-, and high-activity groups based on their level of physical activities, which included everything from running to yard work and washing the kitchen floor.
"A person whose activity level is classified as high typically might engage in several hours of walking, sports or other types of exercise per week, as well as yard work and other household chores," Stehling says.
The researchers took MRI scans of study participants' knees, looking for signs of bone, joint and cartilage damage.
Results showed that people in the high-activity group had much more damage, including cartilage and ligament lesions and buildup of fluid in the bone marrow, than those in the low-activity group.
For example, 93% of people in the high-activity groups suffered cartilage damage vs. 60% in the low-activity group. And cartilage damage was three times more severe in the high-activity group.
The participants' age or sex didn't affect their risk of knee injury, Stehling says.
The researchers are continuing to follow the participants to see if those in the high-activity group actually develop arthritis and if low-impact vs. high-impact activities affect their risk.