Just after 10 a.m. on August 28, more than a thousand runners surged from Orsières, Switzerland, toward Chamonix, France, to compete in the prestigious Orsières-Champex-Chamonix (OCC) ultramarathon.

In what is certainly the pinnacle of the trail running world, Jim Walmsley and Courtney Dauwalter were each greeted by a riveting hero’s welcome from roaring spectators as they ran into the crowded ...