Weight for It……
Every once in a while, a scientific paper is released examining that a conventional wisdom or assumption that just about everyone “knows to be true” and raises serious questions regarding its validity. The current issue of the Journal of Orthopedic and Sports Physical Therapy [July 2020] includes a paper that does just this.
The knee, as many of you know, is the site of the highest percentage of running-related injuries. We’ve covered almost all of them in the series, including “Runner’s Knee” (aka, patellofemoral pain syndrome), “Jumper’s Knee” (patellar tendonitis), and meniscus tears.
I have little doubt that if you asked 100 people if they believe there is a strong connection between knee injuries and excessive body weight (or more specifically, Body Mass Index – BMI), at least 99, if not all 100, would agree that this an accurate statement. Makes sense, right? Physicians and other healthcare providers have forever preached against the “evils” of obesity, both in terms of medical conditions such as heart disease, diabetes, high blood pressure, as well as the supposed detrimental effects on lower extremity joints from greater levels of “pounding.” And this does not apply just to runners, but for just about everyone. Moreover, there is a well-documented association between your generic knee arthritis and excessive body weight. (When I was a student, I attended a lecture by a highly-regarded orthopedic surgeon; he said, half-kidding, that he told all his knee and hip arthritis patients that they needed to lose weight if they wanted to reduce their pain. Of course, he said, hardly any of them ever did, so if they didn’t improve, it wasn’t his fault they didn’t get better…)
I’ve lost count of the number of runners I’ve seen over the years who have volunteered that, perhaps if they lost a few pounds, they would not have their knee pain. I’m sure it would not come as a surprise to you that most of these individuals make ballet dancers look rotund!
So it should not come as a surprise that when a group of Danish researchers asked the question, does excess weight make one more susceptible to running-related knee injuries, their hypothesis going in was that they would find at least a 10% increase in such injuries in runners who are classified as overweight or obese.
But surprisingly, when the team analyzed the pooled results of 4 separate studies that included 571 runners, their findings were just the opposite of their expectations. The proportion of subjects who had sustained knee injuries was 13% lower in overweight and 12% lower in obese runners as compared to normal-weight runners! (Before you get too excited, it should be noted that the study did find that the heavier runners had a higher proportion of lower leg injuries; this paper was concentrating on knee injuries specifically because of the aforementioned association between weight and knee arthritis.)
So, what’s to be made of this? Well, first of all, let’s reiterate that knee arthritis was not one of the conditions defined as a running-related injury. As I’ve noted several times in the past, there is overwhelming evidence that running itself does not inevitably lead to premature knee or hip arthritis. The injuries examined in this study were to other structures (meniscus, tendon, kneecap) of the knee, so the premise of the authors’ hypothesis linking weight and knee injuries may have been unfounded to begin with.
What the findings indicate to me is that factors other than weight may be to blame for the development of these knee injuries. I have tried to explain in the past that I believe faulty biomechanics of the lower extremities – specifically those that pertain to rotational movements – cause most of the injuries we see in runners, including the knee injuries described. Those biomechanical problems are usually related to strength/flexibility imbalances in the hips or foot and ankle. Weight by itself most likely does not influence this.
As is often the case in such studies, the authors outline a number of limitations in their research that gives rise to caution in interpreting their conclusions. But I think there is enough good information here to allow us to stop blaming and focusing on excessive weight for every problem we may encounter.