Le Défi de Boulet - Feins is a loop race in Feins, Ille-et-Vilaine, following a simple rule: complete 6.7 km within one hour, or you are eliminated. All participants restart on the hour, making the challenge the repeated reset as much as the distance, with the race limited to 10 loops.
The course includes 50 metres of climbing and 50 metres of descent per loop, enough to require careful pacing without becoming a mountain race. J2M sports et aventures organizes the event, providing bib pickup on race day, with toilets, parking, and food available. A unique addition is the complimentary support for mental and physical preparation, and nutrition, including dietary monitoring by a nutritionist.