Behavior plan and the intention-behavior gap in physical activity among adolescents and college students: a...

(1) To conduct a meta-analysis on the structure of the TPB extended model to examine the predictive effects of its components on physical activity participation among adolescents and college students; (2) To investigate the moderating effects of key research dimensions, including participant groups, cultural backgrounds, physical activity measurement methods, study designs, and gender composition (proportion of females), on the relationships between variables in the TPB extended model and behavioral models for adolescents and college students physical activity; (3) To test the mediating effects of the TPB extended model; (4) To examine the direct effect of perceived behavioral control on adolescents' and college students' behavior.

A systematic literature search was conducted across multiple databases to identify studies applying the extended Theory of Planned Behavior (TPB) model to physical activity (PA) in adolescents and college students (approximately 10-24 years). A total of 28 articles (including 31 independent samples, with a total of 19,652 unique participants) met the inclusion criteria. Pairwise meta-analyses were performed using random-effects models in CMA 3.0 software. Meta-analytic structural equation modeling (MASEM) was conducted in Amos 24.0, with covariance matrix and harmonic mean constructed based on the summarized correlation matrix. Moderation analyses were conducted to examine the moderating effects of participant group, cultural background, physical activity measurement method, study design, and gender composition. Publication bias was assessed using funnel plots and Egger's regression tests, and methodological quality was evaluated using the adapted Newcastle-Ottawa Scale (NOS-xs).

The TPB extended model explained 54.7% of intention differences, 29.2% of behavior differences, and 28.9% of behavior plan differences. Behavioral intention was found to be a significant statistical mediator variable connecting the three major factors of TPB with behavior, and additional indirect effects have been observed through the sequential pathway of behavioral intention and behavior plan. Moderator analyses revealed that the strength of several TPB relationships was contingent upon participant characteristics (adolescents and college students), cultural background, measurement methods, and study design.

The TPB extended model demonstrates predictive utility for adolescents and college student's physical activities at the aggregate level and can explain, on average, substantial variations in behavioral intention, behavior, and behavior plan across the diverse studies synthesized here. Nevertheless, the extreme heterogeneity (I ² > 90% for many pairwise associations) indicates that effect sizes vary considerably across populations, instruments, and study designs, limiting the generalizability of any single pooled estimate to specific subgroups or settings. In this cross-sectional synthesis, Perceived Behavioral Control (PBC) showed the strongest statistical association with behavioral intention. Behavior plan was also statistically associated with the relationship between behavioral intention and action, and may represent a potential explanatory pathway; however, the predominantly cross-sectional design precludes any causal or temporal inferences. The action path of this model is moderated by participant group, cultural background, measurement method, and study design, highlighting its contextual sensitivity. These findings underscore that PBC and behavior plan may be key variables for inclusion in future intervention designs, although their causal impact on behavior change still remains to be established via controlled trials.