By listing only negative effects, you can make anything sound bad (e.g. <a href="http://en.wikipedia.org/wiki/Dihydrogen_monoxide_hoax" rel="nofollow">http://en.wikipedia.org/wiki/Dihydrogen_monoxide_hoax</a>).<p>It doesn't seem crazy to think that there's such a thing as too much exercise, but there are a couple problems with this top ten list you cite.<p>First, maybe there are right and wrong ways to run a marathon and the people doing it the wrong way have skewed the results of these studies.<p>Second, if running a marathon is bad, then surely running half a marathon is still not good, right?  What about a quarter-marathon?  One mile?  Etc.  I think everyone agrees that there is some amount of running that does more good than harm.  But it's not that helpful to simply say that marathons cause harm without looking at the good (if any) they do and then trying to find the distance that properly balances good and harm.