Аннотация:The present study examined whether self-efficacy mediates the relationship between family social influence and physical activity among youth who have experienced a recent lapse in their physical activity participation. Using a prospective, longitudinal design, participants completed measures of social influence, self-regulatory efficacy and physical activity. Only those participants whose physical activity declined were retained for further analysis. Self-regulatory efficacy partially mediated the relationship between family social influence and physical activity, with self-efficacy mediating 36 percent of the total effect. The results provide support for self-regulatory efficacy as a mediator and provide preliminary insight into the potential mechanisms for preventing lapses in activity from developing into prolonged periods of inactivity within this population.