Why runners don't get knee arthritis
ONE of the most entrenched beliefs about running, at least among non-runners, is that it causes arthritis and ruins knees.
But a nifty new study has found that this idea is a myth and distance running is unlikely to contribute to the development of arthritis.
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.
Researchers at Queen's University in Kingston, Ontario, and other institutions looked more closely at what happens, biomechanically, when we run and how those actions compare with walking.
But before the new study - which was conducted on 14 healthy adult recreational runners, half of them women, with no history of knee problems - scientists had not directly compared the loads applied to people's knees during running and walking over a given distance.
The study found that the volunteers 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 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 developed knee arthritis, said Dr Ross Miller, now an assistant professor of kinesiology at the University of Maryland, who led the study.
Measured over a particular distance, "running and walking are essentially indistinguishable", in terms of the wear and tear they may inflict on knees.
In fact, Dr Miller said, the study's results intimate that running could potentially be beneficial against 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.
"But that's speculation," he said.
The results are also not an endorsement of running for knee health, he 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, which is often called "runner's knee".
But for those of us who are - or hope to be - still hitting the pavement and trails in our twilight years, the results are soothing.
"It does seem to be a myth" that our knees will necessarily wear out if we continue to run, Dr Miller said.