The Relationship Between Physical Activity and Mobile Phone Addiction Among Adolescents: A Cross-Lagged Study

Insufficient physical activity (PA) and problematic smartphone use (PSU) frequently co-occur during adolescence, but whether their prospective association reflects stable differences between adolescents or within-person fluctuations remains unclear. This three-wave longitudinal study examined reciprocal prospective associations between PA and PSU in 1015 Chinese adolescents aged 12–18 years across 12 months, with assessments separated by approximately six months. PA was assessed using the Physical Activity Rating Scale-3, and PSU was assessed using the Smartphone Addiction Scale–Short Version. A random-intercept cross-lagged panel model (RI-CLPM) was specified as the primary analysis, with a conventional cross-lagged panel model (CLPM) estimated secondarily for comparison with previous longitudinal research. In the RI-CLPM, the stable between-person components of PA and PSU were negatively associated (β = −0.681, p = 0.004). At the within-person level, higher-than-usual PA was prospectively associated with lower-than-usual PSU at the subsequent wave (β = −0.117 and −0.108), whereas higher-than-usual PSU was prospectively associated with lower-than-usual subsequent PA (β = −0.257 and −0.189); all four cross-lagged paths were statistically significant. The secondary CLPM showed reciprocal negative cross-lagged associations in the same directions. By separating stable between-person differences from within-person deviations, this study extends longitudinal evidence on the PA–PSU relationship and indicates that the two behaviors are prospectively coupled within adolescents over time. These findings provide a basis for future research and intervention trials that consider PA and problematic smartphone behavior jointly, while causal mechanisms remain to be established.