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.
Key words: exercise, determinants, reasoned action, adolescents
A general consensus exists regarding the benefits of a physically active lifestyle (Bouchard, Shephard, & Stephens, 1994; U.S. Department of Health and Human Services, 1996). Specifically, it has long been accepted that physical activity is important during childhood and adolescence to maintain normal growth and development (Bar-Or, 1983) and establish lifestyle patterns that will reduce the risk factors for health problems in later life (Baranowski et al,, 1992; Williams, Carter, & Wynder, 1981). Research evidence emphasizes the importance of childhood activity as a determinant of physical activity patterns in later life (Dennison, Strauss, Mellits, & Charney, 1988; Pate, Baranowski, Dowda, & Trost, 1996; Powell & Dysinger, 1987). It has also been shown that physical activity involvement is related to other healthy lifestyle patterns in youth (Vidmar, 1992). For instance, active adolescents are less likely to smoke cigarettes than their sedentary counterparts (Aaron et al., 1995). Evidence also exists that p hysical activity is related positively to academic performance (Dwyer, Blizzard, & Dean, 1996; Shephard, 1996). Thus, it logically follows that early identification and modification of physical activity determinants in children and youth has promise for both immediate and long-term benefits for personal and public health and well being. Toward this end a consensus now exists regarding suitable physical activity guidelines for adolescents (Sallis & Patrick, 1994). Developed by representatives from scientific bodies, medical societies, and government agencies, the guidelines call for daily adolescent physical activity with three or more sessions per week lasting 20 min or more each and requireing moderate to vigorous levels of exertion.
Two concepts that have been highly fertile in contributing to understanding adherence to exercise programs or participation in leisure-time physical activity are the theories of reasoned action (Ajzen & Fishbein, 1980) and planned behavior (Ajzen, 1985, 1991). The theory of reasoned action proposes that one can predict an individual's intention to perform a specific behavior from the attitudes held toward that behavior and from a measure of subjective norm (the belief that important others think he or she should or should not perform the behavior in question). Intentions, in turn, are proposed to correlate well with the observed actions (Ajzen & Fishbein, 1980). Recent research using the theory of planned behavior has demonstrated that when volitional control is more problematic, such as in the study of physical activity or exercise, the addition of perceived behavioral control significantly improves the predictive ability of the model (see Godin & Kok, 1996).
Recent reviews of the theories in exercise have found that they provide viable theoretical structures for examining exercise and physical activity in a number of different settings and among most populations (Blue, 1995; Brawley, …