Drawing on semi-structured interviews with older adolescents, this article examines how healthism, ideal body discourses and performative body discourses influence their (non)participation in physical activity (PA) and their identity construction concerning exercise, sport and physical education. We illustrate that body transformation through PA, and related slim body desire and the fear of masculinised female bodies, affect adolescents' decisions to engage in or drop out of sport. Also, a non-hegemonic body shape combined with a display of low physical competence triggers classmate and teachers' rejection and marginalisation, affecting adolescents' construction of embodied identities and preventing them from being active. Finally, adolescents who are competent in sport are less influenced by ideal body discourses than by performative body discourses. We highlight the health promotion effects of these hegemonic discourses and suggest strategies to challenge them.