Abstract
BACKGROUND: Adolescent participation in extracurricular physical activity is pivotal for advancing the "Healthy China" initiative and achieving the United Nations Sustainable Development Goals (SDGs) for Good Health and Well-being. While family social capital, a micro-level dimension of the social determinants of health (SDH), is known to shape adolescents' physical activity behaviors, its specific mechanisms of influence and potential public health spillover effects remain insufficiently clarified. MATERIALS: Based on the SDH theoretical framework, this study employed a stratified random sampling method to investigate 1,218 primary and secondary school adolescents. Structural equation modeling (SEM) and propensity score matching (PSM) were utilized to analyze the influence pathways of family social capital dimensions (structural, relational, and cognitive) on extracurricular physical activity participation and associated health outcomes. RESULTS: Relational family social capital exhibited the strongest positive predictive effect on the weekly duration of adolescents' extracurricular physical activity (β = 0.37, p < 0.001). Cognitive social capital indirectly increased participation frequency through the mediating variable of exercise attitude, with a mediating effect contribution rate of 43.9%. Compared to the control group, adolescents in the high family social capital group demonstrated an 18.5% increase in Z-scores for aerobic endurance, a 4.2% reduction in body fat percentage, and an 11.3% decrease in the detection rate of depressive symptoms. Furthermore, intervention effects showed inter-school heterogeneity: structural social capital had a more significant impact in urban schools, whereas relational social capital played a dominant role in county-level schools. CONCLUSION: Family social capital serves as a core endogenous driver of adolescents' extracurricular physical activity participation. It directly improves physical and mental health indicators and may alleviate pressure on public health services by reducing long-term chronic disease risks. These findings provide empirical evidence for formulating differentiated, family-based sports intervention strategies and promoting health equity among adolescents in the context of global sustainable development goals.