Bidirectional associations and developmental trajectories between physical activity and weight self-stigma among adolescents with high body weight/obesity: A longitudinal study.

Adolescents with overweight/obesity face co-occurring declines in physical activity (PA) and intensifying weight self-stigma (WSS), yet the longitudinal reciprocal dynamics remain poorly understood, particularly outside Western contexts. This three-wave study examined developmental trajectories and within-person bidirectional associations between PA and WSS in 325 Chinese adolescents (Mage = 15.41), using latent growth curve and random-intercept cross-lagged panel models to disentangle stable between-person differences from temporal fluctuations. PA showed a significant linear decrease (β = -.25) while WSS linearly increased (β = .31). Parallel growth analyses revealed that higher initial PA predicted slower WSS accumulation (β = -.22), and higher initial WSS forecasted steeper PA declines (β = -.20). Critically, reciprocal within-person effects emerged only during the academic semester (T1 → T2): deviations above one's typical PA level reduced subsequent WSS (β = -.15), and elevated WSS suppressed later PA (β = -.18), whereas the corresponding cross-lagged effects were not significant during the winter vacation (T2 → T3), underscoring context-dependent temporality. No gender moderation was detected. These findings demonstrate that PA and WSS form a mutually reinforcing loop that is acutely sensitive to environmental structure, informing targeted, phase-sensitive interventions that combine stigma reduction with PA promotion within naturalistic educational settings.