Most climbers who ascend Mont Blanc via the technical Innominata Ridge spend three days reaching the 15,771-foot summit.
Ultrarunner Kilian Jornet did it last fall in eight hours and 43 minutes.
The 25-year-old was recently named one of Outside Magazine's Adventurers of the Year. The magazine noted that this hybrid of climbing and distance running is so new it doesn't have a name yet.
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"What Kilian did on the Innominata Ridge is pioneering a new style of alpinism," Nebraska ultrarunner Anton Krupicka, 29, a two-time winner of Colorado's Leadville 100, told the magazine. "To solo that stuff in eight hours - it's three, four times as fast as anyone's ever done it. It's crazy."
Jornet and the few others involved in this fledgling sport run with a backpack that carries essential gear: crampons, rope and water.
So far, the endurance athletes have focused on shattering solo speed records: last summer, Jornet and fellow runner-climber Andy Anderson of Colorado both ran up and down Wyoming's 13,770-foot Grand Teton in under three hours. It takes most hikers about 20 hours.
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Organized races have taken note, too: A new 50-kilometer mountain run will be held in Big Sky, Mt., this September, and Colorado ultrarunner Dakota Jones is hoping to persuade the U.S. Forest Service to approve a competition in Telluride, Colo., in August that would feature steep climbs and rough terrain.
"I don't think I do this or that sport," Jornet told Outside. "I basically just enjoy being fast in the mountains."
Photo: Killian Jornet and Iker Karrera run in the 20th Diagonale des Fous (the diagonal of the fool) or Grand Raid, a 170-km run on the French island La Reunion in the Indian Ocean. Credit: Getty Images