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Can Too Much Exercise Be Harmful?

Chronic Long-Distance Training May Harm the Heart; Moderate Running Linked With Lower Death Risk, Studies Find
WebMD Health News

June 4, 2012 -- Exercisers who train chronically to compete in marathons, triathlons, and other long-distance events may be hurting their heart health, according to a new report.

"Chronic extreme endurance efforts, like marathons, ultra-marathons, and long-distance triathlons, can cause cardiovascular damage over time," says researcher James H. O'Keefe, MD, director of preventive cardiology at the Mid America Heart Institute at St. Luke's Health System, Kansas City.

"Healthier exercise patterns involve not such extreme duration or intensity," he tells WebMD.

His multi-study review is in Mayo Clinic Proceedings.

In another study, researchers found that running at moderate speeds was linked with a lower risk of death from any cause compared to no running. More intense running didn't yield additional benefit.

That study was reported Saturday at the American College of Sports Medicine annual meeting.

The message is not to fear exercise, but to practice moderation, say O'Keefe and Carl "Chip" Lavie, MD, medical director of cardiac rehabilitation and preventive care at Ochsner Health System, New Orleans. Lavie was involved in both the review and the running study.

"What we don't want to lose sight of is: People who exercise do better than people who don't exercise," Lavie says.

Endurance Training: Research Update

Evidence about the ill effects of chronic training for extreme endurance events is accumulating, the researchers say in the review.

An evolving body of data indicates that chronic training for, and participation in, extreme endurance events ''can cause dilation and stretching of the heart's chambers, especially the atria and right ventricle," O'Keefe says.

The pumping ability of the right ventricle can be reduced. Blood indicators that reflect damage to the heart muscle can increase, he says.

These changes usually return to normal, he says, within about a week. However, if the training is chronic, it may lead to scarring, enlargement, and stiffening of the heart, he says.

There is a risk, too, of developing abnormal heart rhythms such as atrial fibrillation, O'Keefe says. AFib increases stroke risk.

In one of several studies cited in the review, researchers compared 102 healthy male runners, aged 50 to 72, to 102 men who did not run. Each runner had done at least five marathons in the last three years.

About 12% of the marathon runners had heart scarring. It was three times more common in them than in the comparison group.

During a two-year follow-up, the marathoners were more likely to have a heart attack or other heart or stroke-related problem.

An autopsy released after the recent death of legendary long-distance runner Micah True found he had cardiomyopathy, O'Keefe says.

In the condition, the heart becomes enlarged, thick, or rigid.

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