05/23/2012 02:30 pm ET

Phys Ed: Are Marathons Bad For The Heart?

When word circulates that a runner has died of a heart attack, as the inexhaustible ultramarathoner Micah True did last month during a solo wilderness trail run, many people begin to wonder about the healthiness of prolonged strenuous activity. Could marathon training and racing perhaps have damaged the heart muscle of the 58-year-old Mr. True, a lead character in the book “Born to Run”? And, conversely, shouldn’t marathon training have made him — and, by extension, all runners — immune to heart disease?

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