Marathon Running Doesn’t Always Do the Heart Good

b_250_0_16777215_00_images_obgrabber_2013-11_6160867ec6.jpgiStock/Thinkstock (NEW YORK) -- The thousands of runners who took part in Sunday’s New York City Marathon probably believe they strengthened their cardiovascular system by participating in the 26.2-mile run, but a Quebec doctor suggests the strain most likely caused temporary damage to their heart muscles.

Dr. Eric Larose of the Quebec Heart and Lung Institute at Laval University studied 20 marathon runners, aged 18 to 60, who had each run an average of eight marathons. Larose evaluated the athletes before and right after the Quebec City Marathon, and again three months later, and discovered that strenuous exercise can harm heart tissue, causing inflammation, particularly among those runners who had lower fitness levels and less training.

After the race, half of the runners showed a decline in left and right ventricular function.  Those are the pumping chambers of the heart that take blood to the lungs and the rest of the body.  Some of the participants also experienced swelling and reduced blood flow.

The changes in the heart were more common in those runners who had lower fitness levels and less training.  But the damage was temporary.  Larose said the runners with left ventricular decline had returned to their pre-race function three months later.

Larose concludes that training -- not age -- is a predictor of cardiac problems.  The less the runners trained, the more heart changes they experienced.

"When you don't train as you should, you are going to get these changes," he said.

Copyright 2013 ABC News Radio