The Measure of a Mountain: Jim Walmsley’s Evolving Limits

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. 

The course comprised nearly 38 miles of alpine trail with 3,400 meters (11,155 feet) of elevation gain, including a punishing climb toward the Col de Balme high mountain pass in the second half of the race. Running at this elevation requires the body to operate efficiently with less oxygen, which makes preparation at altitude...