Drawing on longitudinal, qualitative research into girls' participation in physical activity and sport in the UK, this article will explore girls' embodied constructions of 'healthy' identities. My research with girls (aged 10-13) found that over the transition to secondary school, classed and gendered healthism discourses had come to powerfully frame girls' sports participation by condoning the achievement of slender embodied femininities through physical activity. The findings suggest that while neoliberal indictments of self-care through physical activity can usefully frame girls' individual 'body projects', these discourses also contribute to a hierarchisation of bodies within physical activity settings and to increasingly narrow standards of acceptable bodies able to take part in physical activity. Within the article, I consider how healthism discourses both regulate and are resisted by the girls as they work to construct physical identities within their school settings.