Journal of North Khorasan

Abstract Background & objective: Physical inactivity is prevalent among adolescents around the worlds. This study tested the ability of the theory of planned behavior )TPB( to predict Physical Activity )PA( among adolescents in a 4-weeks longitudinal study. Materials & Methods: 623 adolescents were randomly selected from eight high schools in Qazvin. TPB measures, and a revised International Physical Activity Questionnaire were measured at baseline and 1-month follow-up. Hierarchical regression analyses were conducted regressing Physical Activity at Time 2 onto TPB. Results: the mean age of the adolescents was 15.5 years and the most of them were girls( 51.2 %(. Past behavior accounted for a significant 57% of the variance in Physical Activity in Step 1of analysis. In Step 2, TPB accounted for an additional 7% with attitude, subjective norms and perceived behavior control as a significant predictor. The analysis resulted in a significant amount of incremental variance accounted for by the intention ( Step 3(. Conclusion: The results of this study demonstrated the theory of planned behavior successfully predicted the most of physical activity's variance among adolescents. Our results suggest that theory-based interventions should be based on the TPB with a targeting on PBC