Reciprocal Associations Between Physical Activity and Life Satisfaction: A Longitudinal Study of Adolescents

<title>Abstract</title> <p>Background Most longitudinal studies examining physical activity and life satisfaction in adolescents rely on the conventional cross-lagged panel model (CLPM), which conflates stable between-person trait differences with within-person change over time. The COVID-19 pandemic provides a naturalistic test of whether the direction and magnitude of this association are context-dependent. Methods This study applied the Random Intercept Cross-Lagged Panel Model (RI-CLPM) to four annual waves of nationally representative Korean panel data (Korean Children and Youth Panel Survey [KCYPS] 2018; N = 2,160) spanning the pre-, acute-, and post-pandemic periods (2018–2021). Results The RI-CLPM demonstrated superior fit relative to the CLPM across all nested model specifications. Life satisfaction exhibited consistent within-person autoregressive stability across all intervals (β = .258 to .305, p &lt; .001). Physical activity showed significant autoregressive continuity at T1-T2 (β = .190, p &lt; .001) and T3-T4 (β = .130, p &lt; .001) but not at T2-T3 (β = .052, p = .105), coinciding precisely with the onset of pandemic-related school closures and mobility restrictions. Cross-lagged effects between physical activity and life satisfaction were small in magnitude and reversed direction across the pandemic timeline: positive within-person associations observed in the pre-pandemic phase (PA→LS: β = .074, p = .017; LS→PA: β = .094, p &lt; .001) became non-significant and subsequently negative as the pandemic progressed (PA→LS: β = − .075, p = .021; LS→PA: β = − .071, p = .045). The between-person random intercept correlation was positive but small (r = .056, p &lt; .001). Conclusions The longitudinal physical activity–life satisfaction association is not a contextually invariant positive effect; its sign and magnitude are conditioned by the socio-environmental circumstances under which physical activity occurs. Theoretical implications for activity-mode specificity, self-determination theory, and conservation-of-resources dynamics are discussed alongside practical recommendations for adolescent health promotion during periods of social dislocation.</p>