Predicting exercise behaviour : extending the theory of planned behaviour with implementation intentions, dispositional variables, and past behaviour

Abstract

The present study investigated exercise behaviour over a six-week period in a theory of planned behaviour context, extended with implementation intentions, dispositional variables, and past behaviour. Two waves of questionnaires were used to measure behavioural intention, perceived behavioural control, past behaviour, and three dispositional variables, that is optimism, self-efficacy and action-orientation, as well as actual performance of exercise behaviour. Implementation intentions were manipulated at Time 1. A total of 214 students at the University of Oslo were assigned to an experimental group (N = 112), who received implementation intention instructions, and a control group (N = 102) who received no instructions. The actual frequency of exercise behaviour was measured at Time 2 and regressed on the selected variables. The results showed that the theory of planned behaviour components intention and perceived behavioural control explained 37% of the variance in exercise behaviour. Implementation intentions failed to add any explained variance or moderate the intention-behaviour relationship. Past behaviour increased the explained variance with 15% and showed mediator and moderator effects on the intention-behaviour relationship. Concerning the dispositional variables, action-orientation increased the explained variance in exercise behaviour slightly with 1%, and moderated the intention-behaviour relationship. Optimism, on the other hand, increased the explained variance by 1%, with only borderline significance. Self-efficacy was found to moderate the intention-behaviour relationship with borderline significance. The results highlight the importance of motivational and habitual processes underlying exercise participation, and suggest that dispositional variables may contribute to the prediction of exercise behaviour. The results may have practical implications concerning exercise interventions.