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Regular exercise can ease the pain and disability of osteoarthritis even if it doesn't result in weight loss, a recent study suggests.

Osteoarthritis, or wear and tear on the joints, is often blamed on excess weight. Extra pounds are believed to put added strain on weight-bearing joints, especially knees, and they break down.

But the new study, which was conducted on lab mice, indicates that weight alone isn't fuelling this inflammatory condition.

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The researchers at Duke University Medical Center in Durham, N.C., began their mouse experiments with two key goals in mind: They wanted to see if mice fed a high-fat diet developed osteoarthritis, and whether exercise provides a protective effect.

The first phase of the experiment went as expected. The mice became obese and showed signs of arthritis in their knees.

When exercise was added to the rodents' regular routine, they didn't lose weight. (The modest amount of physical activity – running on an exercise wheel – wasn't enough to counteract the fat-laden diet.) However, the activity still led to a reduction in arthritis symptoms.

If extra weight had been solely responsible for the joint problems, exercise – without weight loss – should have contributed to further joint damage. But that's not what happened. Pain and inflammation decreased, according to the findings published in the journal Arthritis & Rheumatism.

So how does exercise help? Blood tests conducted on the mice provide a clue. They revealed a variety of changes, including altered levels of cytokines – chemicals that regulate various biological functions.

"Cytokines may be the mechanism by which cartilage breaks down and joint disease occurs," speculated Farshid Guilak, the senior author of the study. "And somehow exercise may change the interaction among cytokines and interfere with the disease process."

A lot more research must be carried out before doctors have a better understanding of osteoarthritis.

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Meanwhile, Dr. Guilak said patients can exercise without worrying that physical activity will make their aching joints feel worse – a common concern that keeps many people sedentary.

"Getting your joints moving helps them a lot and it's actually one of the better ways to relieve pain without drugs," he said.

Indeed, for years, many rheumatologists have been telling their patients to exercise. This study confirms they are on the right track.

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