Physical activity and adolescent anxiety trajectories: a longitudinal analysis of exercise self-efficacy and body image.

Purpose: Adolescent anxiety develops heterogeneously, yet most evidence on physical activity remains cross-sectional and variable-centered. This study examined whether baseline physical activity was associated with differential anxiety trajectory membership across one academic year and whether exercise self-efficacy and body image were related to these associations. Methods: A three-wave longitudinal study was conducted among 1,395 middle school students. Of these, 1,243 provided complete data across all waves. Participants were first stratified into stability-dominant and variability-dominant subgroups based on cross-wave similarity. Anxiety trajectories were then estimated within the variability-dominant subgroup using latent class trajectory modeling. Associations of baseline physical activity with later exercise self-efficacy, body image, and anxiety trajectory membership were examined using linear regression, multinomial logistic regression, and bootstrap-based indirect pathway models controlling for grade, sex, and age. Results: Most adolescents with complete data were classified into the stability-dominant subgroup (76.7%), whereas 23.3% were classified into the variability-dominant subgroup. Within the variability-dominant subgroup, a 3-class solution was retained, comprising Stable Elevated (60.0%), Declining Improvement (18.6%), and Increasing Risk (21.4%) trajectories. Baseline physical activity differentiated subsequent trajectory membership and positively predicted later exercise self-efficacy and body image. Exercise self-efficacy also positively predicted later body image. However, the hypothesized serial indirect pathway through exercise self-efficacy and body image was not consistently supported across trajectory contrasts. Conclusion: Physical activity was associated with differential anxiety trajectory membership, but these associations unfolded within a broader pattern of psychosocial stability. Exercise self-efficacy showed a more consistent role than body image, whereas the hypothesized serial pathway was not robustly supported. Physical activity may therefore be more relevant to developmental positioning across anxiety trajectories than to a simple uniform symptom-reduction model.