Understanding physical activity intention in Canadian school children and youth: an application of the theory of planned behavior.

The purpose of this study was to investigate the efficacy of the theory of planned behavior in predicting physical activity intention in a nationwide sample of Canadian children and youth. The study sample consisted of participants from Grades 3, 5, 8, and 11 from schools across Canada. School participation was determined by means of a randomly stratified sample design. Results show that the direct measures of the theory of planned behavior explained 47% of the variability in the measure of physical activity intention. In addition, notable differences in the relative contributions of the predictor variables of attitude, subjective norm, and perceived behavioral control were found across grade and grade-by-gender subgroups. The present study provides evidence that in a population of children and youth the determinants display a pattern of change developmentally.