Jogging not cause of arthritic knees

One of the most entrenched beliefs about running - among nonrunners - is that the impact causes arthritis and ruins knees.

But studies have not supported that. A recent one finds that distance running is unlikely to contribute to the development of arthritis, precisely and paradoxically because it involves so much running.

It’s easy to understand, of course, why running is thought to harm the knee joint, since with every stride, ballistic forces move through a runner’s knee.

Common sense would suggest that repeatedly applying such loads to a joint should eventually degrade its protective cartilage, leading to arthritis.

But plenty of the available long-term research of runners shows that, as long as knees are healthy to start with, running does not substantially increase the risk of developing arthritis, even if someone jogs into middle age and beyond.

A large cross-sectional study of almost 75,000 runners published in July, for instance, found “no evidence that running increases the risk of osteoarthritis, including participation in marathons.” The runners in the study, in fact, had less overall risk of developing arthritis than people who were less active.

But how running can combine high impacts with a low risk for arthritis has been mysterious. So for another new study, researchers at Queen’s University in Ontario and other institutions looked more closely at what happens, biomechanically, when we run and how those actions compare with walking.

Walking is widely considered a low-impact activity, and many doctors recommend it for older patients, to mitigate weight gain and stave off creaky knees.

But before the new study, which was published in September in Medicine & Science in Sports & Exercise, scientists had not directly compared the loads applied to people’s knees during running and walking over a given distance.

To do so, the researchers recruited 14 healthy adult recreational runners, half of them women, with no history of knee problems. They taped reflective markers to the volunteers’ arms and legs for motion-capture purposes, and asked them to remove their shoes and walk five times at a comfortable pace along a runway approximately 50 feet long. The volunteers later ran along the same course five times, at their usual training pace.

The runway was equipped with motion-capture cameras and pads that measured the forces generated when each foot struck the ground.

The researchers used the runway data to determine how much force the men and women created while walking and running, as well as how often that force occurred and for how long.

In general, the volunteers hit the ground with about eight times their body weight while running, which was about three times as much force as during walking.

But they struck the ground less often while running, for the simple reason that their strides were longer. As a result, they required fewer steps to cover the same distance when running versus walking.

The runners also experienced any pounding for a shorter period of time than when they walked, because their foot was in contact with the ground more briefly with each stride.

The net result of these differences, the researchers found, was that the amount of force moving through a volunteer’s knees over any given distance was equivalent, whether they ran or walked. A runner generated more pounding with each stride, but took fewer strides than a walker, so over the course of,say, a mile, the overall load on the knees was about the same.

This finding provides a persuasive biomechanical explanation for why so few runners develop knee arthritis, said Ross Miller, now an assistant professor of kinesiology at the University of Maryland,who led the study. Measured over a particular distance, he said, “running and walking are essentially indistinguishable,” in terms of the wear and tear on knees.

In fact, Miller said, the study’s results intimate that running potentially could be beneficial in warding off arthritis.

“There’s some evidence” from earlier studies “that cartilage likes cyclical loading,” he said, meaning activity in which force is applied to the joint, removed and then applied again. In animal studies, such cyclical loading prompts cartilage cells to divide and replenish the tissue, he said, while noncyclical loading, or the continued application of force, with little on-and-off pulsation, can overload the cartilage and cause more cells to die than are replaced.

“But that’s speculation,” Miller said. His study was not designed to examine whether running could actually prevent arthritis but only why it does not more frequently cause it.

ON THE OTHER FOOT

The results are not an endorsement of running for knee health, Miller said. Runners frequently succumb to knee injuries unrelated to arthritis, he said, and his study does not address or explain that situation.

One such ailment is patellofemoral pain syndrome, known as “runner’s knee.”

But for those of us who are - or hope to be - still hitting the pavement and trails in the twilight years, the results are soothing. “It does seem to be a myth,” Miller said, that knees will wear out if people continue to run.

ActiveStyle, Pages 27 on 10/07/2013

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