This US investigation assessed physiological and psychosocial variables over a 9-month period of an experimental YMCA-based after-school care programme, “Youth Fit 4 Life” (YF4L), involving 9–12-year-olds. Outcomes are reported for 86 pupils on the YF4L programme and 55 who enrolled in a typical care group for 45 min/day. YF4L is based on social cognitive theory, emphasising mastery over physical activities and the development of self-management/selfregulatory skills to support healthy behaviours. At baseline, 28% of the entire cohort were overweight or obese. At the 3- and 9-month time points, compared with typical care, YF4L was associated with significantly greater improvements from baseline in body mass index (BMI), as well as measures of self-regulation, mood, self-efficacy, cardiovascular endurance and strength. Changes in self-regulation, mood and self-efficacy significantly mediated the treatment type–BMI relationship over both 3 months (R2 = 0.12; p=0.002) and 9 months (R2 = 0.13; p=0.001); change in self-regulation was a significant independent mediator. Changes in BMI and self-regulation reciprocally reinforced one another. Gender did not significantly moderate those relationships.
