Recreational runners may want to train a little more before signing up for a marathon, as Science Daily reports that joining long-distance runs without proper preparation may cause heart damage.

In a study initially published in the Canadian Journal of Cardiology, researchers observed 20 recreational runners between ages 18 to 60 six to eight weeks before a scheduled marathon. The participants were once again tested on the day of the run itself and 48 hours after it.

Based on the MRI and blood sampling results, the researchers found a decrease in function in the left and right ventricles of half of the amateur runners who had low fitness levels. There was also reduced blood flow and swelling of the heart.

"The findings suggest that there may be a minimum fitness level needed beyond which the heart can bounce back from the strain of training and running a long race," concludes senior author Eric Larose of the Institut universitaire de cardiologie et de pneumologie de Québec (IUCPQ), Canada. "Furthermore, these results emphasize the need for proper preparation before recreational distance runners engage in a marathon race."

(Photo by William Murphy via Flickr Creative Commons)