The moderated mediation effect of physical activity on non-suicidal self-injury: the mediating role of perceived stress and the moderating role of parental support.

Objectives: Non-suicidal self-injury (NSSI) has emerged as a significant public health challenge among adolescents globally. Although physical activity (PA) is widely recognized as a potential protective factor for mental health, the internal mechanisms through which it is associated with specific high-risk behaviors like NSSI remain insufficiently explored. This study aims to construct and validate a moderated mediation model to examine the association between PA and adolescent NSSI, the mediating role of perceived stress, and the boundary conditions set by parental support. Methods: Utilizing a cross-sectional observational design and a stratified cluster sampling method, 402 adolescents (198 males and 204 females; mean age = 15.23 ± 1.57 years) were recruited from five middle and high schools (three urban, two rural) in Sichuan Province, China. Participants completed a battery of psychometric instruments, including the Physical Activity Rating Scale-3 (PARS-3), the Perceived Stress Scale-10 (PSS-10), the Inventory of Parent and Peer Attachment (IPPA), and the Deliberate Self-Harm Inventory (DSHI). Data analysis was conducted using SPSS 26.0 and the PROCESS macro (Model 58). Results: PA was significantly and negatively associated with adolescent NSSI (β = -0.58, p < 0.001). Perceived stress partially mediated this relationship, with the indirect association accounting for 36.21% of the total effect. The substantial direct association (63.79%) suggests that PA may also relate to NSSI through other unmeasured pathways, such as speculative neurobiological adaptations or behavioral replacement. Furthermore, parental support significantly moderated the mediated process. Specifically, parental support moderated both the PA -> perceived stress pathway (β = 0.15, p = 0.003) and the perceived stress -> NSSI pathway (β = -0.14, p = 0.005), suggesting that the negative association between PA and stress is stronger under low parental support. Conclusions: PA serves as a potential protective factor negatively associated with NSSI through both direct and indirect statistical pathways. Parental support functions as a critical environmental buffer; for adolescents lacking parental support, PA serves as a crucial compensatory resource for stress management. These findings offer empirical evidence for the development of integrated family-school intervention strategies for adolescent mental health.