The 20th edition of the Ultra-Trail du Mont-Blanc, one of the world’s most demanding mountain ultras, sets off from Chamonix at 17:45 on Friday. About 2,000 runners will attempt the roughly 174-kilometre loop around Mont Blanc—crossing France, Italy and Switzerland and climbing close to 10,000 metres—with a maximum time limit of 46 hours 30 minutes. Four-time winner François D’Haene returns as the headline contender and is regarded by race organisers as a realistic threat to lower the course record he set in 2017. His challenge comes as the sport enjoys rapid growth; France alone hosted more than 6,000 trail-running events in 2022, according to race-calendar data. Organisers say this year’s UTMB also serves as a test bed for lower-carbon race logistics, mirroring broader efforts by endurance events to shrink their environmental footprint. The race is scheduled to finish on Sunday evening, when the winner’s time and any record attempts will be confirmed.