How Big Dog's Backyard Ultra is the ultimate sign of endurance

Out in Bell Buckle, Tennessee, there's a man named Gary Cantrell who brings ultra-marathon runners into his backyard to run in the Big Dog's Backyard Ultra.

Out in Bell Buckle, Tennessee, there's a man named Gary Cantrell who brings ultra-marathon runners into his backyard to run in the Big Dog's Backyard Ultra. The rules of the competition are simple. Runners must complete a 4.167-mile loop every hour and the last one standing wins. SI's Jessica Smetana tells the story of athletes who risk massive injuries to win a small gold coin, inscribed with, "I SURVIVED," on the back.