The practice of recreational sports plays a part in the structuring of mountain regions with regard to several requirements. Following the golden age of winter sports, the challenge of sustaining the French ski resort economy in the 1980s was affected by a diversification of practices. Embodying this "fun" attitude, all-terrain cycling spread into the mountains. The representations and the values underlying it allow us to understand the appropriation of these new forms of practices as much as their co-transformations. The case of Oisans, a territory with mythical status thanks to the historical passage of the Tour de France, allows us to put the impact of these new methods into perspective. The events, the shaping of the territory, the professional transformations which are seeds of a sociocultural mutation, and the conflicts linked to integrating the practice determine the impact of this activity, which has now become an identity marker of mountain regions.