aged²" target="_blank">Middle-aged¹ men and women may be risking arthritis³ if they overdo⁴ their exercise regime, research suggests.

研究显示，中年男女超出合适的运动体制可能有患关节炎的风险。

Can exercise be too much of a good thing?

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（膝盖） damage.

Running and jumping may also do more damage to cartilage（软骨） and ligaments（韧带） than swimming and cycling, researchers said.

One arthritis（关节炎） charity said it was important to keep fit and most people would not have any problems.

Osteoarthritis（骨关节炎） - the most common form of arthritis - is a degenerative（变性的，退化的） joint⁵ disease that causes pain, swelling⁶（膨胀） and stiffness and affects 8m people in the UK.

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（损害，障碍） and other abnormalities in the cartilage and ligaments.

The damage seen was associated solely⁷ with activity levels and was not age or gender⁸ 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 outweighed⁹ 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."