Everyone who's not a numbskull accepts that some exercise is good. The question here is, is there such a thing as too much running, and if so, how much is too much?
Well, too much by what standards? There are two flaws you should look out for when you see these kinds of studies. First of all, the best studies are the ones that look at the association between [some exposure, in this case running] and all-cause mortality. If you're reading this post, I imagine it's more likely because you want to know if running will make you live longer, rather than you suddenly worried if your troponins went up after a 5-miler. Studies which use other endpoints (like cardiac markers or signs of inflammation as Thompson et al 2011, or imaging like Wilson et al 2011) might actually be overstating the risks because they're assuming that these things translate into the outcomes that we care about, like longevity, and they might be wrong. (That is to say: yes, Wilson convinces you that lifelong endurance athletes have more fibrotic hearts. Unless we're fairly certain this means they'll die sooner, who cares?) On the other hand, they might not be stating the risks strongly enough - because what if running is bad, and damaging the heart isn't the only way it hurts you? Unlikely though it is, if running is bad for you, and it (at least partly) kills you by messing up your spleen and you're just looking at the heart, you're not going to capture all the carnage.
Second, some studies are limited by non-generalizeable results. That is to say, they look at hardcore ultramarathoners, or they look at the effect of marathons on un-fit people. You might look at these papers and say, "Well, before they told me that, I figured it wasn't a good idea to show up to a marathon without reasonable training, and I also don't run an ultra every month." In other words, how much can any of it be applied to the rest of us?
So that's why I like this paper. In the Journal of the American College of Cardiology Schnohr et al provide all-cause mortality evidence that frequent, strenuous jogging is the same as no exercise at all in terms of mortality benefit. The optimal time and frequency: 1 to 2.4 hours per week; 2 to 3 times per week, at a slow to average pace. The downside is that for many of us traily types, that's very much on the low side. The upside is that those weeks when you only get out 2-3 times? They're just fine for extending your life. I thought this sounded familiar, and looked back over my previous posts, and sure enough Schnohr presented the same conclusion in 2012 at the European Society for Cardiology from data gathered in the Copenhagen City Heart Study. Encouragingly, the mortality benefit he reported in 2012 was on the order of 6 years of extra life!
Tomas G. Neilan, MD; James L. Januzzi, MD; Elizabeth Lee-Lewandrowski, PhD; Thanh-Thao Ton-Nu, MD; Danita M. Yoerger, MD; Davinder S. Jassal, MD; Kent B. Lewandrowski, MD; Arthur J. Siegel, MD; Jane E. Marshall, RDCS; Pamela S. Douglas, MD; David Lawlor, MD; Michael H. Picard, MD; Malissa J. Wood, MD. Myocardial Injury and Ventricular Dysfunction Related to Training Levels Among Nonelite Participants in the Boston Marathon. Circulation. 2006; 114: 2325-2333
M. Wilson, R. O'Hanlon, S. Prasad, A. Deighan, P. MacMillan, D. Oxborough, R. Godfrey, G. Smith, A. Maceira, S. Sharma, K. George, and G. Whyte. Diverse patterns of myocardial fibrosis in lifelong, veteran endurance athletes. J Appl Physiol (1985). 2011 Jun; 110(6): 1622–1626. Published online 2011 Feb 17. doi: 10.1152/japplphysiol.01280.2010PMCID: PMC3119133
Eric Larose, Canadian Cardiovascular Congress 2010.
Peter Schnohr, MD, DMSc; James H. O'Keefe, MD; Jacob L. Marott, MSc; Peter Lange, MD, DMSc; Gorm B. Jensen, MD, DMSc. Dose of Jogging and Long-Term Mortality: The Copenhagen City Heart Study. J Am Coll Cardiol. 2015;65(5):411-419. doi:10.1016/j.jacc.2014.11.023
European Society of Cardiology 2012 EuroPRevent2012 Meeting (Press Release).