Contestants take a selfie before for the start the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France August 31, 2018.
Jim Walmsley of the U.S., compatriot Zach Miller and Kilian Jornet of Spain run in the Col de Voza during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Chamonix, France August 31, 2018.
Competitors rest during the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Dolonne near Courmayeur, Italy September 1, 2018.
A competitor crosses a stream during the 16th Ultra-Trail du Mont-Blanc (UTMB) race at the Val Ferret near Courmayeur, Italy September 1, 2018.
Xavier Thevenard of France celebrates winning the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France September 1, 2018.
Contestants wait for the start the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France August 31, 2018.
Competitors climb during the 16th Ultra-Trail du Mont-Blanc (UTMB) race at La Balme near Chamonix, France August 31, 2018.
Competitors run at the Lake Combale during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Courmayeur, Italy September 1, 2018. Picture taken with a long exposure.
Xavier Thevenard of France runs in the Col de Voza during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Chamonix, France August 31, 2018. Picture taken August 31, 2018.
Competitors run through the Mont-Blanc massif in the Alps during the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France, September 1, 2018. Picture taken on September 1. REUTERS/Toby Melville
Contestants wait wait for the start the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France August 31, 2018.
A competitor rests during the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Dolonne near Courmayeur, Italy September 1, 2018.
Competitors climb the Val Ferret during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Courmayeur, Italy September 1, 2018.
Jim Walmsley of the U.S. runs in the Col de Voza during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Chamonix, France August 31, 2018.
Competitors run in the Col de Voza during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Chamonix, France August 31, 2018.
Competitors climb the Val Ferret during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Courmayeur, Italy September 1, 2018.
Xavier Thevenard of France celebrates winning the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France September 1, 2018.
Kilian Jornet of Spain runs in the Col de Voza during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Chamonix, France August 31, 2018.
Luzia Buehler of Switzerland waits for the start the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France August 31, 2018.
A contestant lights a candle in the St-Michel church before the start of the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France August 31, 2018.
Competitors climb during the 16th Ultra-Trail du Mont-Blanc (UTMB) race at La Balme near Chamonix, France August 31, 2018. Picture taken with a long exposure.
Competitors run at the Lake Combale during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Courmayeur, Italy September 1, 2018.
Competitors run at the Lake Combale during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Courmayeur, Italy September 1, 2018.
Xavier Thevenard of France celebrates after winning the 16th Ultra-Trail du Mont-Blanc (UTMB) race in Chamonix, France September 1, 2018.
Competitors warm up by a fire at the Lake Combale during the 16th Ultra-Trail du Mont-Blanc (UTMB) race near Courmayeur, Italy September 1, 2018.
Ultra-marathon through the Alps
Runners punish themselves on a 106-mile race through the Alps in the 16th Ultra-Trail du Mont-Blanc, regarded as one of the most difficult foot races in the world.
