Middle-aged men and women may be risking arthritis if they overdo their
exercise regime, research suggests.
A US study of more than 200 people aged 45 to 55 and of "normal" weight found
those doing the most exercise were the most likely to suffer knee damage.
Running and jumping may also do more damage to cartilage and ligaments than
swimming and cycling, researchers said.
One arthritis charity said it was important to keep fit and most people would
not have any problems.
Osteoarthritis - the most common form of arthritis - is a degenerative joint
disease that causes pain, swelling and stiffness and affects 8m people in the
UK.
People with higher physical activity levels may be at greater risk for
developing knee abnormalities
Dr Christoph Stehling University of California, San Francisco
It is more common in women, and the risk increases with age and weight.
Presenting the findings at the annual meeting of the Radiological Society of
North America, the researchers said their study included people who had not
reported any previous knee pain.
Activity
Based on a questionnaire designed to work out how much exercise they do,
participants were split into low-, middle- and high-activity groups.
A typical high-activity individual would do several hours of walking, sports or
other types of exercise per week, as well as gardening and other household
chores.
They then underwent MRI scans of the knee, looking for tears, lesions and other
abnormalities in the cartilage and ligaments.
The damage seen was associated solely with activity levels and was not age or
gender specific, the researchers said.
And it also seemed to be linked to the type of exercise a person did, although
the researchers said this needed to be looked at in other studies.
Study leader Dr Christoph Stehling, a researcher at the University of
California, San Francisco said: "Our data suggest that people with higher
physical activity levels may be at greater risk for developing knee
abnormalities and, thus, at higher risk for developing osteoarthritis.
"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.
"Conversely, low-impact activities, such as swimming and cycling, may protect
diseased cartilage and prevent healthy cartilage from developing disease."
A spokeswoman for the Arthritis Research Campaign said that the gains of
exercise far outweighed any potential risks.
"We have known for years that certain high impact sports and jobs are
associated with an increased risk of osteoarthritis, particularly of the knee,
but for the vast majority of people exercise is good, not only for the
cartilage but for total body health.
"Most people can exercise without any problems, but if you have had a joint
injury or torn cartilage or ligaments you should be cautious about
weight-bearing exercise, and swimming and cycling may provide a better option
for you."