Running Is One More Thing Where Less Is More: Is there such a thing as too much running?

Outrunning the grim reaper, slowly.

Physicians have long understood the important of exercise for good health. Hippocrates observed, “Walking is the best medicine”, and 2,000 years of experience and research confirms the singular importance of exercise for our species. So much so that, if it were possible, as a physician I would write a prescription for exercise for every patient as they leave my office.

But if we think of exercise as a powerful “prescription medicine” we need to answer a few questions. For example, what is the optimal dose, and how often should “exercise” be taken? Is more always better? If this were true, exercise would be an unusual sort of medicine, because most medicines have a therapeutic range above which they become toxic.

Is there such a thing as too much running?

To fix ideas, consider running: Is there an optimal dose of running? Is there such a thing as too much running?

Oddly, the best folks to ask are not runners, but epidemiologists. A very well-done study published in the prestigious Journal of the American College of Cardiology by Schnohr and colleagues¹ looked at exactly this question by following 5,000 healthy subjects (1,000 joggers and 4,000 non-joggers) over a period of 12 years, carefully recording health outcomes. As expected, sedentary individuals were the most likely to die, almost 6 times(!) more likely to die than those who exercised. Fortunately, it didn’t take much jogging to be promoted out of the dangerous sedentary group: jogging as little one hour each week at a slow pace qualified as “jogging”. The real surprise, however, was that it was this group of “underachievers” that had the lowest mortality rate of any group. Far lower than the sedentary group, of course, but also less than the moderate jogger group. Even more surprising, it was the strenuous joggers who had the worst outcome, possibly even worse than the sedentary group(!). Here’s the figure from the paper that summarizes these findings. (Note that although the two different models are adjusted for different covariates, the results are similar, suggesting that the covariates aren’t what is driving the result. Hazard ratio is a measure of the likelihood of dying, where higher is more likely to die. The confidence intervals are wide because relatively few people (145) died during the study.)

The revelation that for jogging “less is more” came as a surprise, and this paper has now been cited almost 600 times in the medical literature. Exactly why those who exercised the most were most at risk for early death isn’t known, but a recent paper in the journal Nature² found that “… In veteran endurance athletes, myocardial fibrosis is common and associated with an increased burden of ventricular ectopy. Possible mechanisms include inflammation and blood pressure.”

The Schnohr study was done in Denmark, but this study was repeated in Dallas, Texas in 2014 with the same results.³ The Texan authors conclude: “Running, even 5-10 minutes per day and slow speeds <6 mph, is associated with markedly reduced risks of death from all causes and cardiovascular disease.”.

 

The real surprise, however, was that it was this group of “underachievers” that had the lowest mortality rate of any group.

Of course, arguing for a “less is more” approach to running presupposes the reason you’re running is to live longer. If your goal is to run further or run faster, adding some more intense training methods will be more effective than occasionally slowly running slowly not very far. But for many people, a healthy cardiovascular system and longer life are exactly the point, and unfortunately this group may have been discouraged from taking up running by the emphasis on running ever faster and further, a story pushed by companies motivated to sell more, and more expensive, running gear.

The idea of “running slowly” seems oxymoronic, but the idea has been around over a century. The roots of slow jogging can be traced back to the work of Dr. Hiroaki Tanaka an exercise physiologist working at Fukuoka University in Japan in the mid-20th century which lead eventually led to “Niko Niko” as slow jogging is known in Japan. Over the last 20 years there have been efforts to popularize “ultra-slow running” by the International Slow Jogging Federation. Here is this short public health YouTube video about the advantages of slow running⁴ which has been viewed over 3 million times.

As it happens, there are also reasons that performance-oriented runners might want to make slow running (zone 2”) part of their training routine.⁵ For example, running slowly allows the body to stay well oxygenated while running, which creates more mitochondria within cells as well as promoting the development of capillaries between cells, changes that not only improved aerobic capacity but also translate to better performance at higher intensities: more oxygen thruput, more energy output.

And then there’s this perspective: Flipping the script, maybe it’s not that running is good for us, but rather that being sedentary is bad for us. This would account for the dramatic role of even modest exercise, because it doesn’t take much movement to be promoted to the “non-sedentary” category.

But why is being sedentary so toxic for humans? Chimpanzees share 98.8% of their DNA with us, so our cellular machinery is almost identical to that of our chimp cousins. And yet chimps require almost no exercise to stay healthy and maintain body fat levels near zero. Why is it that humans do very poorly without regular exercise? David E Lieberman, the Lerner professor of biological sciences at Harvard University, has offered his Costly Repair Hypothesis⁶. The idea is that following exercise we ramps up the mechanisms that repair damage caused by exertion, but with an overshoot that also repairs any preexistent damage. As Lieberman puts it: “Exercise is like scrubbing the kitchen floor so well after a spill that the whole floor ends up being cleaner. The modest stresses caused by exercise trigger a reparative response yielding a general benefit…. In short, we never evolved to counter many aging processes without physical activity, which activates repair responses.”

Of course, the Costly Repair Hypothesis is just a hypothesis. But as Lieberman presents it, his theory is a plausible consequence of evolution, and thus makes sense to biologists, because among biologists it’s an article of faith that, “Nothing in biology makes sense except in the light of evolution.”⁷.

So, when you breeze past a grey-haired soul on the bike path plodding along with their slow, flatfooted gait you might wonder for a moment if they might not actually be winning the real race. Because science says that they are. This isn’t surprising, because they’ve got skin in the game. They’re not running to win; they’re running for their lives.

 

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¹Dose of jogging and long-term mortality: the Copenhagen City Heart Study
²Identification of non‑ischaemic fibrosis in male veteran endurance athletes, mechanisms and association with premature ventricular beats
³Slow Jogging: science-based natural running for weight-loss, health & performance benefits
⁴What Is Slow Running and Does It Work?
⁵Active Grandparenting, Costly Repair
⁶On Citing Dobzhansky about the Significance of Evolution to Biology