Is Too Much Running Bad for You?

"Can You Get Too Much Exercise?", asks Gretchen Reynolds in the New York Times on Wednesday.  This question and other similar questions have been asked and debated extensively over the past year.  Can you get too much exercise?  Probably so, but it is clear is that exercise improves heart health in most people and reduces the risk of developing heart disease or dying of heart disease. The questions of too much and how much is too much, remain to be answered. Back in November of last year, Dr. James O'Keefe suggested that one should not run more than 25 miles a week and never faster than 8 minutes a mile.
 http://indorgs.virginia.edu/MuscleClub/OKeefe_JH_article1%2B2.pdf

  The graph above is from that article.  The data, which was taken from a study published in The Lancet, appears to show that the benefit of vigorous exercise levels off after about 50 minutes of activity.  In reality the data did not end at 50 minutes, it went on well beyond that point.  Such that at 120 minutes the hazard ration for all-cause mortality reduction was at .55 noticeably better than at .48 or so at 50 minutes.  For a more thorough discussion take a look at Alex Hutchison's column in the November 28, 2012 Runners World.
 http://www.runnersworld.com/health/too-much-running-myth-rises-again

Wednesday's NYT article focuses on study involving athletes who can completed the Vasaloppet, a grueling 56-mile cross-country ski marathon held each March in northwestern Sweden.  The study found that among male participants of a 90 km Vasaloppett, a faster finishing time and a high number of completed races were associated with higher risk of arrhythmia. This was mainly driven by a higher incidence of atrial fibrillation and brady arrhythmia. No association with supra-ventricular tachycardias or ventricular tachycardia/ventricular fibrillation/cardiac arrest was found. And while the risk of arrhythmia increased, the authors state that "participants in Vasaloppet have lower mortality than the general population and that mortality decreases with increasing number of races."

  -Mortality amongst participants in Vasaloppet: a classical long-distance ski race in Sweden. J Intern Med 2003;253:276-283. doi:10.1046/j.1365-2796.2003.01122.x.

  So your risk of arrhythmias increases slightly with very high levels of exercise.  However your risk of dying goes down.  Hmm.  Guess that means I should keep on doing my long runs, my fast runs and my marathons.  As Dr. Anderson says,"Carry on as usual, but remember to listen to your body and seek a doctor if you experience any symptoms from your heart."
http://well.blogs.nytimes.com/2013/07/24/can-you-get-too-much-exercise/?_r=0