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.
BLOG: What It's Like to Fall Off a Cliff
"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.