Have fun at the L.A. Marathon Sunday but don't drop dead.

Seriously. Turns out those ironic tales about hardcore athletes and fitness fanatics taking their last steps during grueling runs might not be so rare. Running could actually be bad for your health.

Seriously. Well, there is a catch …

… and that is, it would take lots and lots of running for your exercise to become a health risk.

A study published last month in the Journal of Applied Physiology looked at male athletes and couch potatoes young and old and concluded that half the oldsters (over 50) who had trained long and hard in events such as marathons had heart problems.

The men had a high rate of heart muscle scarring called myocardial fibrosis (not good).

A summary:

An unexpectedly high prevalence (50%) of myocardial fibrosis was observed in healthy, asymptomatic life-long veteran male athletes, compared to zero cases in age-matched veteran controls and young athletes. This data suggests a link between life-long endurance exercise and myocardial fibrosis that requires further investigation.

But experts caution not to take this to mean that you shouldn't exercise regularly or even run the occasional marathon if you're healthy. But it does say something for those older ultra-marathon types.

Dr. Paul Thompson, the chief of cardiology at Hartford Hospital, tells the New York Times this:

Too much exercise has not been a big problem in America. Most people just run to stay in shape, and for them, the evidence is quite strong that endurance exercise is good.

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