Effects of a 12-week physical activity and health behavior change protocol (Youth Fit For Life), delivered in 3 day/week after-school care and 2 day/week physical education formats, were assessed and contrasted with African American children, ages 9 to 12 years, in an experimental study. Body Mass Index, percent body fat, and muscular strength were significantly improved in both formats for both boys and girls, with effect sizes larger in the after-school care condition. Significant improvements in mood and self-appraisal factors were also associated with participation in the protocol in both formats, with effect sizes somewhat larger in the physical education format. Increases in days per week of voluntary, moderate-to-vigorous physical activity were significant and similar in both conditions (Mchange = .71 and .75 days/week, ps < .01). Multiple regression analyses indicated that changes in scores of physical appearance, physical self-concept, exercise self-efficacy, and perceptions of the overall self explained a significant portion of the variance in changes in voluntary physical activity sessions over 12 weeks, R2 = .24 to .73, ps < .001. Implications for development of an adequate explanatory model of physical activity in children, evidence-based physical activity intervention design, and reduction in overweight preadolescents, were suggested. © International Journal of Clinical and Health Psychology.
