People who exercise often are less likely to develop the condition than inactive "couch potatoes", they say.

Osteoarthritis is traditionally thought of as developing from "wear and tear" on the joints.

Painless running or other activities which are aerobic and make you fit help keep you vigorous for longer

Professor Jim Fries, Stanford University

But US researchers say it is only the "tearing" or injury that is the problem.

They found that those who get the most benefit run between six and 20 miles a week.

Osteoarthritis is a degenerative form of joint disease, which affects around two million people in the UK.

Disability

The researchers, from Stanford University, California studied 538 members of a running club and 423 people who never did any exercise.

All were aged around 58 and had similar levels of health when the study began in 1984.

Each year, they were assessed by doctors for disability and pain.

The progression of osteoarthritis was checked using X-rays and doctors looked for signs of osteoporosis.

By the end of the study, 20% of those who took no exercise had pain and disability compared to 5% of the runners.

Runners also had greater bone density and less bone mineral loss.

Amongst non-runners, women were more likely to experience disability than men.

Twisting

Professor Jim Fries, an expert in healthy ageing who led the research, told a national newspaper: "We know now that painless running or other activities which are aerobic and make you fit help keep you vigorous for longer.

Sitting around and being a couch potato is the worst thing you can do for your health

Arthritis Research Campaign spokeswoman

"You are four times better off in avoiding disability, and that's what we all worry about."

Professor Fries, who presented his research to a medical conference in Sorrento, Italy, added: "Running or jogging does not increase the risk of osteoarthritis, even though traditionally we thought it was a disease of wear and tear.

"It's the wearing that's OK and not the tearing, because it's important to avoid injury."

But he said the same was not true of activities which involved tears around the joints, caused by twisting and turning, such as football.

Professor Fries added: "This accelerates the development of osteoarthritis, particularly of the knee.

"Even ballet dancers are at increased risk for osteoarthritis - at the base of the big toe."

Damage

A spokeswoman for the Arthritis Research Campaign told BBC News Online: "It's certainly a myth that exercise wears out joints, but excessive running can put the joints under a lot of strain, and may lead to injuries.

"Footballers are at greater risk of osteoarthritis than runners, because of the damage they do to their joints from injury."

She added: "If you've already got a painful knee because of osteoarthritis we'd recommend that you did a less weight-bearing form of exercise such as swimming or cycling.

"Sitting around and being a couch potato is the worst thing you can do for your health - whether or not you've got arthritis, and exercise is probably the best thing."

But Neil Betteridge, of Arthritis Care, said: "Everybody's experience of arthritis is unique.

"It's probably too simple to be clearly for or against running in terms of how arthritis may develop.

"For someone with no cartilage or who is obese, it could easily be very damaging to be running, so people should always take advice from their doctor."

Mr Betteridge added: "It's encouraging to have it confirmed that aerobic exercise is beneficial for the bones and joints."

Philip Newton, director of the Lilleshall Sports Injury Centre in Shropshire, said running did benefit the joints because it was weight-bearing exercise, and encouraged the lubrication of joints through the production of synovial fluid.

He added: "Most of us lead fairly sedentary lives, so running and sport probably makes up for that, and redresses the balance a bit."