EXPLORING MOTIVATIONAL MECHANISMS IN EXERCISE BEHAVIOUR : Applying Self-determination theory in a person-centred approach

Abstract: Involvement in physical activity (PA) and exercise behaviour is multifaceted and depends on bidirectional correlations between multiple factors; one avenue to increase the understanding of sustainable exercise behaviours would be to employ a motivational perspective. In this thesis, this was done by placing the primary focus on Self-determination theory (SDT) as a person-centred approach to study the motivational mechanisms believed to impact exercise behaviour based on the SDT process model. Study 1, conducted in a cross-sectional design, included 1,091 members of a web-based exercise service. Based on sophisticated mediation analysis, the results support the hypothesized associations between latent constructs and exercise behaviour in the related steps of the SDT process model. Moreover, moderating effects were discovered, demonstrating that these associations could differ in different subgroups based on gender and age. The results of Study 1 thereby represent a first indication that exercise intervention design might benefit from slightly different approaches when addressing different demographical groups like gender and age. Study 2 was conducted in a two-wave RCT design to test an SDT-informed intervention on 64 voluntary participants. Components of Motivational interviewing (MI), the Relapse prevention model (RPM) and Cognitive behavioural therapy (CBT) were used as practical application guidelines to deliver the intervention content. Results showed intervention effects on exercise level, exercise intensity and motivation quality as well as mediating effects of the RAI (Relative Autonomy Index; an index of the degree of self-determination), and identified regulation in relation to exercise behaviour. The experimental group also demonstrated significantly lower levels of extrinsic motivation than the control group post-intervention. Besides strong support for applying the basic tenets of SDT in the exercise domain, there are some main findings in this thesis. First of all, self-determined motivation was found to act as a mediating variable in the relationship between psychological need satisfaction and exercise, and these patterns of indirect effects differed across age and gender. This indicates that mechanisms in the SDT process model could vary (qualitatively) depending on subgroup, which carries potential implications for practice. Second, the results of Study 2 also provide evidence that the mediating mechanisms of the process model could be manipulated in an intervention, e.g. by creating need-supportive environments facilitating internalization and subsequent exercise behaviour. Furthermore, both studies demonstrated that identified regulation plays a prominent role in the motivational processes, supporting the significance of promoting internalization in activities like exercise. Finally, this thesis represents prospective value for the utility of employing a polytheoretical approach in exercise intervention design, more specifically regarding the prosperous outlooks in combining SDT with other theories and methods.