In July 2014, a shy 14-year-old named Lynzi Doke edged herself into a mob of very fit runners and very big donkeys on the main street of Fairplay, Colo. She felt sick to her stomach. This is a big mistake, she realized, but it was too late: A shotgun blasted, the donkeys stampeded, and the World Championship Pack Burro Race was underway.
Lynzi had to sprint just to avoid getting trampled. Jostling around her were more than 50 men and women, all of them running side by side with their own galloping animals. Lynzi tightened her fist around the lead rope of Chuggs, a beast of a burro she’d borrowed that outweighed her by a good 700 pounds, and tried to breathe in the thin mountain air. Looming ahead were 15 miles of dirt trail, climbing to a peak at more than 11,000 feet.
Lynzi had never run that far in her …