With some studies showing the health benefits of running—good cholesterol levels, improved blood pressure—may be offset by heart conditions like plaque buildup in arteries and arrhythmia in extreme athletes, doctors are divided on whether there's such a thing as too much exercise. While one doctor says, "there is compelling evidence that there's no upper limit," another tells the Wall Street Journal, "why wouldn't there be a relationship between over exercise and heart disease?"
"I don't want anyone to read that exercise can be bad for you," says a columnist for TheHeart.org. "Some folks do tons of exercise and are protected. Some folks probably have some individual susceptibility to it. I'm a big believer in short intervals of high intensity." Recent research indicates that any benefit runners see drops off beyond 30 miles a week, the Journal notes. Still, a veteran marathoner says he's not worried by the blurring line between runners and the not-so-healthy among us. "There are guys who live to be 100 smoking cigarettes and eating cheeseburgers." Click for the full piece. (Read more exercise stories.)