Abstract
BACKGROUND AND OBJECTIVES: The negative impact of depression on adolescents' school social adaptation has been widely confirmed. However, the underlying mechanisms, particularly the synergistic roles of sleep quality and physical activity, remain inadequately explored. This study aims to construct a moderated mediation model to examine the mediating effect of sleep quality between depression and school social adaptation, as well as the moderating effect of physical activity in this pathway. METHODS: A cross-sectional survey design was employed, with 2,354 adolescents (1,098 male, 1,256 female) from six provinces in China participating via convenience sampling. The Patient Health Questionnaire (PHQ-9), Pittsburgh Sleep Quality Index (PSQI), School Belonging Scale (SBS), and Physical Activity Rating Scale (PARS-3) were used to assess depression, sleep quality, school social adaptation, and physical activity, respectively. Mediation and moderation effects were tested using the SPSS PROCESS macro. RESULTS: Correlation analysis revealed a significant negative correlation between depression and school social adaptation (r = -0.410, p < 0.001). Mediation effect testing indicated that sleep quality partially mediated the relationship between depression and school social adaptation. Depression not only directly predicted school social adaptation negatively (β = -0.430, p < 0.001) but also indirectly weakened school social adaptation through its impact on sleep quality (β = -0.294, p < 0.001), which, in turn, positively predicted school social adaptation (β = 0.261, p < 0.001). Moderated mediation analysis further revealed that physical activity significantly moderated both the first half of the "depression → sleep quality" pathway and the direct path from depression to school social adaptation, suggesting that higher levels of physical activity effectively buffer the negative effects of depression on sleep quality and school social adaptation. CONCLUSIONS: Sleep quality is a crucial mediating mechanism through which depression affects school social adaptation, while physical activity plays a positive moderating role in this process. The findings suggest that encouraging adolescents to engage in regular physical activity may serve as an effective intervention strategy to improve sleep quality, alleviate depressive symptoms, and ultimately enhance their school social adaptation. As a primary goal, the abstract should render the general significance and conceptual advance of the work clearly accessible to a broad readership. References should not be cited in the abstract. Leave the Abstract empty if your article does not require one-please see the "Article types" on every Frontiers journal page for full details.