Running does not wreck knees (probably)

On Monday I shared (on Facebook etc) a study by Ponzio et al showing that “science challenges the assumption that relentless ‘pounding’ on the road is hard on joints.” Specifically, in a survey of 675 marathoners:

• No link between current arthritis symptoms and their running history.
• Lower rate of arthritis than the general population. (No matter how much they ran, they had the same low rate of arthritis: about 9%, compared to 18% in non-runners. 😮)

That was a popular item. Good science news usually is.

This is not the only data on this subject, as I well knew, so I went digging for the right kind, the “prospective” kind, produced by following a bunch of runners over time and tracking their arthritis whether they keep running or not. This is ultimately the only way the “running doesn’t wreck knees” thing can be proved.

There’s not a lot of that kind of data to find, but there is Chakravarty et al., which is quite good. After following a few dozen older runners and non-runners for many years — most for more than a decade, some as long as twenty years — 32% of the non-runners ended up with severe arthritis versus only 20% of the runners. And the runners started with 7%!

“Severe OA may not be more common among runners.”

Indeed, it was clearly less common in this study.

What flaws did this study have though? It was prospective, but also tiny. You might well see different results in another few dozen runners just by fluke. But small is not always bad.

(Nerdy clarification: You don’t need to put many people in a shower to prove that it’s an efficacious moistening technology — the “effect size” does the job. “All five of the study subjects were maximally moistened.” This is why we don’t generally bother testing things with obviously huge effect sizes. You only need statistical power to demonstrate subtler effects … like small differences in the incidence of arthritis in runners over many years.)

Still, Chakravarty did acknowledge that size was a limitation here (among several others):

“Much larger studies involving hundreds to thousands of healthy older adults followed for several decades are needed to determine if long-distance running may be associated with a modest decrease in incidence or severity of radiographic OA.”

So we still don’t know, and we may never “know.” There is another prospective trial in the works, with 200 subjects (though only followed for four years). But thousands? For decades? Don’t hold your breath!

And don’t worry much about your knees if you’re a runner. Because the evidence we have, while it may fall short of proof, is quite persuasive.