Researchers say running too much can be just as unhealthy as being a couch potato.
Scientists say people who run at a fast pace for a total of more than four hours a week have about the same risk of dying as those who are sedentary.
Those with the lowest risk of dying are people who run about an hour and a half a week at a slow to moderate pace -- roughly five miles per hour.
Researchers from Denmark say people who push their bodies too hard may essentially undo the benefit of exercise.
