This article aims to study the process of conversion to bodybuilding in order to understand how some gym enthusiasts progressively organise their lives around this activity. Our observations, drawn from an ethnography of a gym and thirty semi-structured interviews with different profiles of gym-goers in French-speaking Switzerland, suggest that the grip that bodybuilding takes on individuals results from processes akin to conversions. Two paths to conversion - consonant and introspective - are identified. They correspond to distinct uses of bodybuilding, which do not have the same consequences in the practitioners' life courses. While consonant conversions stabilise life courses by reinforcing an occupational status, introspective conversions inflect them significantly.