The determinants of physical activity participation for mothers of young children are only beginning to be understood. The aim with this study was to further this understanding by exploring motherhood as a socially and culturally constructed identity linked to physical activity participation.Discursive psychology was used to theorize mother identities as subject positions constructed within discourse(s), and explore the implications for one woman's physical activity participation, through an in-depth case study approach (see Yin, 2009).A newly active 35 year old woman with two young children, husband and activity partner, were interviewed over 16 weeks. Critical discourse analysis (see Wetherell, 1998) of nine interviews was used to explore the constructive nature of language and the effects by identifying the discourses within which mother identities were constructed.Two primary discourses were identified: a patriarchal discourse of the family and a liberal feminist discourse. Participants drew upon these discourses to position the woman's identity as a good mother and/or super mother. Based on the behavioural practices linked to discourses and the subject positions/identities (e.g., good mothers place children's needs over their own), a situation came into being which made physical activity participation difficult.This study contributes towards understanding motherhood and physical activity participation by attending to social and cultural discourses. By constructing mother identities within a patriarchal discourse of the family and a liberal feminist discourse, physical activity barriers of time, fatigue and the family functioned in nuanced ways, and were not easily surmounted.