The Connecticut personal-injury lawyer cracked three vertebrae when he slipped during a race last December. He pulled a hamstring in Tampa two months later, and again in Mississippi a week after that. He nearly passed out in the parched hills of South Dakota in August, finishing last by two hours. In October, he got lost in the woods of Indiana when organizers cleared away the markers. "It's an obsession," he says. "No different than gambling, drinking or doing drugs."
Mr. DeFronzo is part of a proud subculture of self-styled "mega marathoners," people who run hundreds of the 26.2-mile races. Three Germans, a Finn and a Japanese woman are known to have clocked more than 1,000 marathons apiece -- that is 26,200 miles, about 1,300 miles more than the circumference of the earth. The record holder, 74-year-old Horst Preisler, has run 1,636 marathons.