A runner sits in a church prior to the start of the 170 km Mount Blanc Ultra Trail (UTMB) race around the Mont- Blanc crossing France, Italy and Swiss, on September 1, 2017 in Chamonix. The 15 th Ultra- Trail du Mont- Blanc (UTMB) is a mountain ultramarathon with numerous passages in high altitude (>2500 m) and in difficult weather conditions (night, wind, cold, rain or snow). It takes place once a year in the Alps, across France, Italy and Switzerland. (Photo by Jean-Pierre Clatot/AFP Photo)





2300 runners wait for the start of the 170 km Mount Blanc Ultra Trail (UTMB) race around the Mont- Blanc crossing France, Italy and Swiss, on September 1, 2017 in Chamonix. (Photo by Jean-Pierre Clatot/AFP Photo)





2300 runners wait for the start of the 170 km Mount Blanc Ultra Trail (UTMB) race around the Mont- Blanc crossing France, Italy and Swiss, on September 1, 2017 in Chamonix. (Photo by Jean-Pierre Clatot/AFP Photo)





2300 runners take the start of the 170 km Mount Blanc Ultra Trail (UTMB) race around the Mont- Blanc crossing France, Italy and Swiss, on September 1, 2017 in Chamonix. (Photo by Jean-Pierre Clatot/AFP Photo)





Second- placed Spanish athlete and former Mount Blanc Ultra Trail (UTMB) winner, Kilian Jornet, is cheered on by spectators during the 15 th edition of the Mount Blanc Ultra Trail on September 1, 2017 near Chamonix. (Photo by Denis Balibouse/Reuters)





Lights of ultra- trailers competing illuminate the way on September 1, 2017 in Les Contamines Montjoie, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





Ultra- trailers enter in a refreshment post as competing on September 1, 2017 in Les Contamines Montjoie, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





In this long exposure photo, lights of ultra- trailers competing illuminate the way on the Balme path, on September 1, 2017 in Les Contamines Montjoie, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





In this long exposure photo, lights of ultra- trailers competing illuminate the way on the Balme path, on September 1, 2017 in Les Contamines Montjoie, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





In this long exposure photo, lights of ultra- trailers competing illuminate the way past the Combal lake, on September 2, 2017 in Courmayeur, Italy, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





Ultra- trailers compete at sunrise on September 2, 2017 in Courmayeur, Italy, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





Ultra- trailers compete past the Combal lake at sunrise on September 2, 2017 in Courmayeur, Italy, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





Ultra- trailers massages his feet at a refreshment post on September 2, 2017 in Courmayeur, Italy, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





Ultra- trailers eat and rest at a refreshment post on September 2, 2017 in Courmayeur, Italy, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





An Ultra- trailer eats and rests at a refreshment post on September 2, 2017 in Courmayeur, Italy, during the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland. (Photo by Jeff Pachoud/AFP Photo)





Participants celebrate after crossing the finish line of the 15 th edition of the Mount Blanc Ultra Trail (UTMB), a 170 km race around the Mont Blanc crossing France, Italy and Switzerland, on September 2, 2017 in Chamonix. (Photo by Jean-Pierre Clatot/AFP Photo)