Extending the Theory of Planned Behavior in the Exercise Domain: A Comparison of Social Support and Subjective Norm. (Research Note-Psychology)

Article excerpt

Key words: structural equation modeling


Ajzen's (1991) theory of planned behavior (TPB) has emerged as one of the dominant social cognitive frameworks for understanding exercise motivation and behavior. The TPB provides a parsimonious explanation of informational and motivational influences on behavior and can be considered a deliberative processing model. The hypothesized proximal determinant of volitional behavior is one's intention to engage in that behavior. Intentions reflect a conscious plan or decision to enact the behavior. The TPB tries also to predict incompletely volitional behaviors by incorporating perceptions of control over performance of the behavior as an additional predictor (Ajzen, 1991). Perceived behavioral control (PBC) is the individual's perception of the extent to which performance of the behavior is easy or difficult (Ajzen, 1991). Further, PBC is also hypothesized to influence behavior indirectly through intentions, along with attitudes and subjective norms. Attitudes are the individual's overall evaluations of performing the behavior. Subjective norms consist of a person's beliefs about whether significant others think he or she should engage in the behavior and are assumed to assess the social pressures on the individual to perform or not to perform a particular behavior.

Quantitative reviews have consistently supported the utility of the TPB in the exercise domain (Godin & Kok, 1996; Hausenblaus, Carron, & Mack, 1997). However, the construct of subjective norm has not performed well in explaining exercise intentions across studies when controlling for attitude and PBC, typically being either nonsignificant or of small significant magnitude. Given the poor performance of subjective norm in exercise research, some researchers have suggested that it may not be the most theoretically relevant social influence construct in the exercise domain (Courneya & McAuley, 1995a, 1995b; Courneya, Plotnikoff, Hotz, & Birkett, 2000). Courneya and colleagues (Courneya & McAuley, 1995a, 1995b; Courneya et al., 2000) have argued that social support may provide for a greater understanding of exercise motivation and behavior.

The conceptual distinction between these two social influence constructs is that subjective norm refers to the perceived pressure to perform a behavior that comes from observing what important others say or do, whereas social support implies the perception of assistance in performing the behavior (Courneya et al., 2000). The theoretical argument of Courneya et al. (2000) for why social support should be superior to subjective norm in the exercise domain is due to exercise behavior not being under complete volitional control (i.e., not capable of being done at will, or free of practical constraints). That is, subjective norm may be the most relevant social influence construct for behaviors that are under complete volitional control, because for such behaviors a person only needs to know whether important others approve of the behavior. By definition, they do not need any help. For behaviors that are incompletely volitional, however (e.g., exercise), it is likely that assistance from others for performing the b ehavior (i.e., social support) would be helpful beyond knowing they approve of the behavior. Any relationship between these concepts is hypothesised to occur from common exogenous concepts, similar to the tenets of relationships between attitude, subjective norm, and PBC in the TPB proper (Ajzen, 1991).

Only two studies have directly compared the relative utility of subjective norm and social support in the exercise domain (Courneya & McAuley, 1995a; Courneya et al., 2000), and, unfortunately, both have significant limitations. Courneya and McAuley (1995a) used a small, homogeneous sample (i.e., in exercise behavior status) of fitness class participants who completed at least 8 weeks of a 12-week program. …