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Small study found cardiac changes, but they were reversible and less likely with proper training

By Kathleen Doheny

HealthDay Reporter

THURSDAY, Oct. 31 (HealthDay News) -- The thousands of runners who will take part in the New York City Marathon on Sunday most likely believe they are strengthening their cardiovascular system by participating. But new research suggests the strain of a 26.2 mile-run can temporarily damage heart muscle.

That's what Dr. Eric Larose, from the Quebec Heart and Lung Institute at Laval University, found after studying 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.

It turns out strenuous exercise can harm heart tissue, causing inflammation and other problems, particularly among runners who had lower fitness levels and less training, Larose reports in the October issue of the Canadian Journal of Cardiology.

However, he is quick to stress that "there is no permanent damage." Even so, he said, ''there is a cost to running a marathon, there is a cost to everybody."

At the peak of their training, the men and women in Larose's study put in about eight hours of running and logged about 38 miles a week, on average. Larose used MRIs, blood tests and other measures to assess heart function among the runners.

After the race, half of the runners showed a decline in left and right ventricular function -- defined as the operation of the pumping chambers of the heart that take blood to the lungs and the rest of the body.

When a big area of the heart was affected, there was also swelling and reduced blood flow.

The heart changes were more common in those runners who had lower fitness levels and less training. But the damage was temporary. For instance, the 10 runners with left ventricular decline had MRI scans three months later, and all had returned to their pre-race function.

"Age was not a predictor" of cardiac problems, Larose said. Training was. The less the runners trained, the more changes in the heart.

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

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