Before we get to the new stuff, let’s just make sure we’re on the same page with regard to the old “running will ruin your knees” thing. It won’t. Numerous studies have compared groups of runners and non-runners over the course of many decades, and found no evidence that runners are more likely to develop knee osteoarthritis or need knee replacements. In fact, in many studies runners seem to be less likely to develop knee problems, perhaps due to their lower weight, reduced systemic inflammation, and the ability of cartilage to adapt and get stronger in response to regular exercise.



That’s all great, but it doesn’t answer another important question. What if you already have knee osteoarthritis, meaning that your cartilage—the shock absorber between the bones of your upper and lower legs—has started to degenerate? After all, just because running doesn’t cause osteoarthritis, that doesn’t mean it makes you immune. At this point, your knee joint is no longer working the way it’s supposed to. If you keep running, will you hasten the progression of the disease?



Given that over 30 million Americans have osteoarthritis, this is a big question. And the answer, from a scientific perspective, is that we don’t know for sure. Logic suggests that if the joint is already compromised, the high stresses that result from running could worsen the wear-and-tear on the cartilage. But so far there has been very little evidence on which to base any conclusions.



That’s why a new study in the journal Clinical Rheumatology, from a group led by Grace Lo of Baylor College of Medicine, is worth digging into. It draws on a big multicenter study called the Osteoarthritis Initiative, which followed nearly 5,000 people in Pawtucket, Columbus, Pittsburgh, and Baltimore for about a decade. In that group, there were 1,203 people over the age of 50 who had osteoarthritis in at least one knee, of whom 138 happened to be runners throughout the study period.



The subjects underwent a bunch of diagnostic tests, including X-rays, to determine how severe their knee osteoarthritis was. These tests were repeated four years later. So the question is: did those who ran during that period of time have a faster progression of their symptoms than those who didn’t run? No, they didn’t. Here’s what the researchers wrote:

Contrary to what we expected, we found little evidence to suggest that running is harmful in this cohort... Among individuals at least 50 years of age with knee OA [i.e osteoarthritis], running was not associated with longitudinal worsening knee pain or radiographically defined structural progression. Additionally, runners also had more improvement in knee pain compared to non-runners, suggesting that there may be a benefit to running from a knee health perspective in people who have knee OA.

If you look at a measure called “joint space narrowing,” which indicates that the bones are getting closer together because the cartilage is disappearing, 23.6 percent of the non-runners got worse during the study period, while just 19.5 percent of the runners got worse. Similarly, 29.0 percent of the non-runners reported new frequent knee pain, compared to just 26.8 percent of the runners. Conversely, 39.1 percent of the non-runners reported improvements in their knee pain, compared to 50 percent of the runners. When you adjust for other characteristics like age and BMI, it turns out that the runners were about 70 percent more likely to see improvements in their symptoms.



All this is great, but let’s not get carried away. We have very little information about how much mileage the runners logging, or what other differences there may have been between the runners and non-runners. Clearly it’s possible that those who were able to keep running were healthier in some way—although the researchers did look for this possibility, and found that at baseline the runners and non-runners had very similar levels of disease progression and similar BMIs.



One thing that’s very important to emphasize is that these runners weren’t instructed to go forth and run as much as they wanted. They were given no specific instructions at all about running, so they were presumably following their own common sense and the advice of their doctors. Were they running shorter distances, or less frequently, than they used to? Were they stopping and walking home if their knees started bothering them more than usual during a run? Maybe, but we don’t know.



Getting a knee replacement, or living with the pain and compromised mobility of a severely arthritic knee, is no joke, so I’m really hesitant to make any suggestions that might hasten the progression of anyone’s condition. On the other hand, one of the serious consequences of osteoarthritis is that it generally leads to a reduction in physical activity, which in turn leads to elevated risk down the road of other chronic conditions like heart disease and diabetes. For example, one recent study found that osteoarthritis-induced difficulty in walking was associated with a 30-percent increase in the risk of heart attacks, strokes, and other cardiovascular events.



You might argue that if your knees go bad, you should err on the side of caution and take up “joint-friendly” aerobic exercise options like cycling or swimming. That’s eminently reasonable, but not everyone has easy access to a pool or lives in a climate where you can conveniently cycle all year. You can overcome all these objections with sufficient motivation, but in practice, the fact remains that if you take away a popular and convenient exercise option, some people are going to exercise less, with predictable health consequences. So we don’t want to forbid running without considering all the options.



This new study doesn’t tell us that you can run through osteoarthritis with impunity. But I think it does offer some tentative support for the sort of advice I’ve heard from a number of “running-friendly” doctors who I’ve asked about this. They suggest, in essence, letting your symptoms be your guide. That will probably mean modifying how long, how often, and perhaps how fast you run. It may mean trying different shoes or a different running surface, or strengthening your hips and quads, to see if that affects the load on your knee. But it doesn’t mean simply quitting cold-turkey. If you’re able to find a running routine that’s compatible with your osteoarthritis symptoms, these results offer some reassurance that even if your knees are already giving you trouble, you’re still not ruining them by running.

My new book, Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance, with a foreword by Malcolm Gladwell, is now available. For more, join me on Twitter and Facebook, and sign up for the Sweat Science email newsletter.