Move more, scroll less? Physical activity, smartphone use, and subjective body shape perception in adolescents: within-person associations in gender-stratified analyses.

INTRODUCTION: Subjective body shape perception is an important adolescent health issue linked to psychological well-being and weight related behaviors. This study examined within-person associations among subjective body shape perception, physical activity, and smartphone use separately among Korean adolescent boys and girls.

METHODS: Using five-wave data from the Korean Youth Health Behavior Panel Survey (2019-2023), we estimated two-way fixed-effects models controlling for time-invariant individual characteristics and wave-specific factors. The analytic sample included 4,518 adolescents (boys: 2,341; girls: 2,177), contributing 18,721 observations.

RESULTS: Among boys, within-person increases in physical activity were associated with lower subjective body shape perception scores (B = -0.0074, p < 0.05), whereas weekday and weekend smartphone use were not significantly associated with subjective body shape perception. Among girls, increases in weekday smartphone use were associated with higher subjective body shape perception scores (B = 0.0129, p < 0.05), while physical activity was not associated with subjective body shape perception. In additional models, physical activity was associated with lower smartphone use scores among girls on both weekdays (B = -0.0422, p < 0.001) and weekends (B = -0.0294, p < 0.01).

DISCUSSION: These findings suggest that physical activity, smartphone use, and subjective body shape perception may be connected in behavioral patterns observed separately among boys and girls. Future research and intervention studies may consider gender-sensitive approaches that integrate physical activity promotion, smartphone use awareness, and media literacy to support healthier body-related perceptions during adolescence.