Biology suggests that decades of running should invariably blow out your knees. Scientists are trying to understand why that doesn’t happen.
First, the bad news. A sophisticated new model shows that if you start running at age 23 and put in less than two miles a day, there’s a 98 percent chance that your knees will fail by the age of 55. Now, the good news: that doesn’t actually happen in real life. In fact, as I and many others have repeatedly pointed out, the evidence suggests that running is neutral at worst, and possibly even helpful, for the long-term health of your knees. So the real question—and it’s an interesting one—is why runners’ knees don’t fail more than average.
The basic problem is that cartilage, the rubbery material that provides shock absorption between the bones in your knee joint, has no blood vessels or nerves. For that reason, it’s generally considered pretty much inert and unable to repair itself. Over a lifetime of loading, it gradually wears down until the bones are grinding against each other. That’s knee osteoarthritis, the most common joint problem in the U.S., which affects about 10 percent of men and 13 percent of women over the age of 60.
In recent years, though, there’s been pushback against the view that cartilage is just an inert lump. Back in 2006, a bioengineering researcher named Bahaa Seedhom hypothesized that cartilage could actually respond and adapt to the stresses imposed by day-to-day activities, an idea he dubbed “cartilage conditioning.” In fact, he suggested that a lack of joint stress might explain why sedentary people develop knee osteoarthritis. More recently, University of California Davis researcher Keith Baar has suggested that connective tissues, including cartilage, do have self-repair abilities that can be triggered by the right combination of exercise and diet.
A new study in the open-source journal PeerJ, by University of Maryland biomechanist Ross Miller and his former doctoral student Rebecca Krupenevich, explores how these various factors might come together to explain why runners don’t all end up in wheelchairs. It’s a modeling study that combines the measured properties of cartilage and the forces involved in running and walking to predict when knees should fail with and without the existence of self-repair and adaptation abilities in the cartilage. The punchline: there’s good reason to think that, like so many other parts of your body, your cartilage really does get stronger the more you use it.
Read the full article at Outside Magazine by clicking here.