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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
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Runners and Death Risk Study

For the running study, the researchers tracked nearly 53,000 men and women enrolled in the Aerobics Center Longitudinal Study. Each had a medical exam at the Cooper Clinic in Dallas in the years 1971-2002.

The men and women answered lifestyle questions about exercise, alcohol intake, and smoking. Researchers had information on their weight, blood pressure, cholesterol, and other health measures.

About 27% were runners. They reported how often they ran, how fast, and how many days per week.

The follow-up period varied, but averaged 15 years.

During that time, runners overall had a 19% lower risk of dying from any cause compared to non-runners.

A lower risk of death from any cause was found for runners who:

  • Ran less than 20 miles a week
  • Ran at speeds of six to seven miles an hour (about a 10-minute mile)
  • Ran two to five days a week

Those who ran more miles a week at faster paces, or on more days than five, did not have any additional survival benefits, Lavie found.

The study was funded by the National Institutes of Health and an unrestricted research grant from the Coca-Cola Company.

Exercise Studies: Perspectives

Although a number of studies have focused on heart problems among endurance athletes, it does not prove cause and effect, says Aaron Baggish, MD, associate director of the Cardiovascular Performance Program at Massachusetts General Hospital.

"It's been known for decades these people [who train chronically for endurance events] aren't immune to heart problems," he says. "Whether the exercise causes the heart problems isn't yet known."

The athletes studied represent a small subset of people who push the envelope above recommended levels, he tells WebMD.

Baggish reviewed the findings for WebMD.

His research, published earlier this year in The New England Journal of Medicine, found that the risk of cardiac arrest during long-distance races is relatively low and often tied to pre-existing conditions.

Over a decade, he reported, one in 184,000 participants in full or half marathons had a cardiac arrest. Those who run a full marathon are at higher risk.

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