ST. LOUIS (AP) -- Everyone knows that exercise is good for you. But is it possible to exercise too much?
The St. Louis Post-Dispatch reports that a growing body of evidence suggests that it might be.
At least two studies in recent years have found permanent scar tissue and structural changes in the hearts of otherwise healthy men who are avid marathoners. Another study showed that running up to 20 miles a week at an easy pace prolonged life, but running more and at higher intensity produced diminishing results.
Many hard-core endurance athletes say they aren't buying it.
The number of endurance athletes has risen sharply in recent years. The growth of endurance sports is so new that there isn't a lot of research on what it does to the heart.