Why Don’t More Runners Get Knee Arthritis?

We hope you’re well aware there’s no evidence that running increases your risk of developing osteoarthritis in your knees. In fact, studies have found lower rates of knee arthritis in runners than in the general population.

But while we’re happy this is the case, honesty compels us to admit we sometimes think, “Really? How can that be the case, given the impact forces of running?”

The answer might come from two unique aspects of the running gait – short ground contact time and long swing phase – suggests research from Medicine & Science in Sports & Exercise.

Fourteen healthy adults, with no history of knee trouble, walked and ran at self-selected speeds, using as cues the speed at which they walk down the street and adopt when running for exercise. (Most of the participants were regular runners.) Researchers measured impact forces, including peak force on the knee joint and what they called load per unit of distance travelled, or the overall force on the knee in covering a given distance walking or running.

As suspected, the peak load during running was three times greater than during walking. But the load per distance unit travelled was the same.

This finding, the researchers write, could explain why runners aren’t at increased risk of knee osteoarthritis. In their words:

“[T]he duration of load application and the distance covered per loading cycle offset the relatively high peak joint load of running, such that the load accumulated per unit distance travelled is no greater in running than it is in walking. In addition, running has a relatively long swing phase as well as a flight phase, absent from walking, during which joint loads are quite small.

While this result does not imply that runners are at a reduced risk of knee osteoarthritis compared to non-runners, it offers a biomechanical explanation for why running does not seem to increase the risk of osteoarthritis even though peak joint loads in running are very high.”

Other researchers have suggested that runners’ on-average lower weight than most people helps to reduce arthritis risk. In addition, there’s preliminary evidence that excess fat tissue can send out inflammatory signals that might increase arthritis risk.

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