Keep Running Past the Age of 40 and Your Knees Will Fall Apart! True or False?

I'm an enemy of received wisdom, especially on the subject of what constitutes proper care of one's knees, because there are so many mistaken beliefs out there.

For example, you often hear: Keep running long enough and you'll wreck your knees.

After all, how can all that pounding be good for joints where bones meet, their endings protected only by thin pads of cartilage? And if your knees naturally wear out over time, why hasten the inevitable by subjecting them repeatedly to the high-force activity of distance running?

That's the received wisdom on knees and running. The truth appears to be quite different.

While assembling a bibliography for my book about recovering from chronic knee pain, and sorting through my many files, I came across an article by Gretchen Reynolds that I saved a while ago. Dated Aug. 11, 2009, it appears online at the New York Times Well blog. The provocative title: "Can Running Actually Help Your Knees?"

The opening is attention-grabbing:

An article in Skeletal Radiology, a well-respected journal, created something of a sensation in Europe last year. It reported that researchers from Danube Hospital in Austria examined the knees of marathon runners using M.R.I. imaging, before and after the 1997 Vienna marathon. Ten years later, they scanned the same runners’ knees again. The results were striking. “No major new internal damage in the knee joints of marathon runners was found after a 10-year interval,” the researchers reported.

At first blush, this seems incredible. Of all classes of runners, marathoners train the longest; the race itself of course covers 26.2 miles. Over many years of running, their cartilage should be pounded to dust, right?

To be fair, a skeptic might say, "Not so fast! Perhaps the marathoners were relatively young and thus better able to withstand the stresses (just wait til they get older!). Or they may have been the equivalent of professional athletes, with efficient and streamlined bodies. Who else could run so far, so often?"

Yes, good points, but what about this second study that Reynolds cites:

Stanford University followed middle-aged, longtime distance runners (they didn't have to be marathoners). They were largely in their 50s and 60s (no spring chickens there). The trial went from 1984 to 2002. At the end, the knees of the runners were compared with those of a control group, about the same age, who didn't run.

At the time of their first exams, 6.7 percent of the distance runners had mild arthritis in their knees, as opposed to none of the control group subjects. Which seems to be an argument for inactivity.

Except, by the end of the study, the results reversed. Only one in five runners showed signs of arthritic changes in their knee joints; that contrasted with one in three non-runners. Severe arthritis hobbled almost one in ten non-runners, but only one in fifty runners.

What could explain this?

The article suggests that the knee may develop a "motion groove" (those who read my book will discover me discovering that movement is the magic ticket to knee health). Cartilage adapts to the load of running. I would add further: the tissue gets stronger and stiffer and better able to cope with ordinary daily activities without complaining and becoming sore.

Reynolds tosses in a caveat at the end of her article. Once a runner becomes injured, the "exquisite balance" implied by that "motion groove" can become disrupted, leading to a "degenerative pathway" that causes cartilage to wear down and fall apart -- and then comes pain and arthritis. (I've purposefully put some of these phrases in quotations because I'm not totally on board with the author's analysis here -- I smell a Structuralist lurking -- but that's for another time.)

Injury risks do abound for runners and must be guarded against at every turn. Gaining too much weight is a no-no. Being an inconstant runner -- someone who takes off a few months, then tries to pick up at his old level of intensity -- could lead to problems. Ambition can get you in trouble (for example, suddenly going from running three miles twice a week to ten miles three times a week as you begin training for a race). Stubbornly running through early pain signals is stupid.

But running sensibly doesn't appear to be a knee killer. It may help your joints, in fact (though my exercise of choice is cycling, which is easier to do within knee-safe bounds).

SKEPTIC'S CORNER: If you read the comments after the Reynolds article (299 of them!), you will see skeptics weighing in with arguments that can be summarized along these lines: (1) there is selection bias at work, as the runners were all healthy individuals (2) the runners weighed less than the subjects in the control group (3) anyone who is in their 50s or 60s and still running long distances has, through genetics and anatomy, superior knees and cartilage to begin with.

My thoughts, point by point: (1) The study's authors did recognize the possibility of selection bias, as the runners were indeed all healthy, but two things should be noted. First, could running be part of the reason for that good overall health (exercise has been proven to boost the immune system)? Second, osteoarthritis of the knee isn't considered systemic (unlike, say, rheumatoid arthritis), and so how much effect does good health have on one's knees, if any?

(2) The runners had only a "slightly lower BMI," according to the authors. Yet that difference at the outset is a BMI of 22.3 for runners vs. 24 for non-runners (the gap is maintained through the study), according to a table included with the report. For two six-foot men, that translates into a 164.5 lb. runner and a 177-lb. non-runner. That is significant, unfortunately, and I would say is the biggest flaw in the methodology because of the well-established relationship between excess weight and arthritis.

(3) This, to me, is the least convincing argument. Remember, at the outset, 6.7 percent of the runners had mild arthritis, while none of the non-runners did. If the runners really benefited from superior cartilage/knees, then why did they have worse knees at the beginning and better knees at the end? Also, if you drill down into the results, 44.4 percent of the runners complained of a previous knee injury versus 35.9 percent of the non-runners. So why was that injury figure 20 percent higher for the runners if they started out with superior knees and cartilage?