This summer, an international team of endurance athletes and ultra-runners will attempt a record-breaking relay run around Mont Blanc, Western Europe's highest peak. The athletes will begin at sunrise on June 21, the Summer Solstice and longest day of the year, and race until the sun sets. They have 15 hours, 41 minutes, and 35 seconds to complete a 103-mile course around Western Europe's most substantial peak.

The grueling format – dubbed Race the Sun – is the brainchild of ASICS, who is sponsoring the event. To make the 15:41:35 time limit, each competitor will need to output maximum effort during his portion of the relay – essentially red-lining the entire stretch. With 9,600 total vertical feet on a highly technical trail in unpredictable weather conditions, the task may very well prove impossible.

The attempt will begin in Chamonix, passing through France, Italy, and Switzerland. Backpackers complete this trail in seven to nine days. Ultra-runners race it at the annual Ultra-Trail du Mont Blanc, considered to be the most difficult foot race in Europe. Xavier Thevenard, the 2013 winner, crossed the finish line in 20 hours and 34 minutes. Non-professional runners take 30 to 45 hours.

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Thevenard will return to Mont Blanc for Race the Sun. He is part of a four-man team dubbed Team Ultra Trail that includes Japanese elite runner, Kota Araki; 100-mile world record holder, Jonas Buud; and former trail running World Champion, Thomas Lorblanchet. Team Ultra plans to divide the distance into sections ranging from 17 to 29 miles each.

"Returning to Mont Blanc and being a part of this momentous challenge is something I had only ever dreamed about," says Thevenard. "I have had the opportunity to train and race against some of the world's most elite trail runners and now we are joining together and combining strengths."

A second team, Team Enduro, is taking a different approach. This group consists of seven elite athletes from different endurance disciplines: World Champion Triathlete, Briton Tim Don; Austrian extreme distance runner, Christian Schiester; Spanish trail runner and cross country skier, Genis Zapater; American trail runner Megan Kimmel; French runner, Sylvaine Cussot; and long distance runner, Gert Theunis. Team Enduro plans to divide the run into 10- to 18-mile splits.

Which team, if either, will rise to the challenge, and which discipline (ultra-running versus endurance sports) fares better on the course, will be proven on June 21 on Mont Blanc.