If Scooby Doo was a runner and, if he paid attention to recent stories in the media concerning the benefits and risks associated with running, he would right about now be uttering (barking?) his famous catch phrase.

An article that appeared a few weeks ago in The Wall Street Journal soon after became the topic of an interview with its author on the National Public Radio sports program Only a Game.  The WSJ article summarizes a review paper that appears in the British medical journal, Heart.  That paper draws some surprising – and what will no doubt be, for many, disconcerting –conclusions.

The authors of this paper acknowledge that many of our most cherished assumptions about the health benefits of running are true; in particular, they note that the claim that regular running decreases one’s mortality risk as compared to sedentary individuals is basically accurate, while at the same time challenging the idea that this is universally true.

Based on data gathered from a number of studies, this paper argues that too much, or too fast, running may actually be detrimental to cardiovascular health. They claim that research is now showing that chronic, extreme exercise –which they define as greater than 25 miles per week or running consistently faster than 8 miles per hour (7:30 per mile) – appears to cause excessive “wear and tear” on the heart.  They describe this as structural changes in heart muscle and electrical remodeling which may offset some of the cardiovascular benefits and longevity improvements that moderate physical activity confers.  Among the structural changes noted, the most significant appear to be increased fibrosis (scarring) of critical regions of the heart, increased coronary artery calcification, and large-artery wall stiffening.

The authors take pains to note that they are not to saying that chronic extreme exercise will kill you, but it may erase many of the health benefits gained through more moderate exercise.  They argue that the evidence indicates a“sweet spot” for exercise of between 5-25 miles per week at a pace of 6-7 miles per hour to realize the aforementioned benefits of coronary health and increased longevity.

So what is one to make of these rather sobering arguments?  Well, as an orthopedic physical therapist, my area of (alleged) expertise is limited for the most part to the musculoskeletal system of the body.  And, although I (again, allegedly) personally have a heart, I make no claim to more than an average knowledge of cardiology.  I do, though, believe I have enough understanding of statistics and research design to make some observations on the significance of this paper.

First, I will stipulate that most of the studies cited in this paper had very large sample sizes (e.g., one followed over 52,000 subjects for three decades), which is always a good thing to have when you’re trying to determine true differences between groups. But none of the studies were of the experimental variety; in other words, they did not randomly assign individuals to two or more groups with specific tasks to perform (run or not run; run less than or more than 25 miles per week).

All of the results of these studies are what we classify as correlational findings; they show only an association between various factors, not a cause-and-effect.  As such, the weakness is that there may be other factors that are not accounted for that may explain these associations.  For example, it has long been established that individuals with so-called Type-A personalities are more likely to see reduced longevity due, perhaps, to increased stress.  One could make a plausible argument,therefore, that those individuals driven to participate in extreme exercise over a long period of time fall within that personality type, which raises the question– Is it the exercise or the personality causing the effects described in the paper?

The WSJ article mentions that there are other experts who challenge some of the statistical analysis used by the researchers (Paul Thompson, an eminent sports cardiologist and former elite marathoner, accuses the authors of the paper of manipulating the data to satisfy “an agenda”), so there is some justification for taking their recommendations at face value.  There is enough there, though, to give one pause and to perhaps heed the words of Ken Cooper, the “father of aerobics,” who years ago stated “If you are running more than 15 miles per week, you are doing it for some reason other than health.”


O’Keefe JH, Lavie CJ, Run for yourlife…at a comfortable speed and not too far. Heart. Nov. 29, 2012