Background/Purpose: Moderate-to-vigorous physical activity (MVPA) is recommended for the treatment and management of physical and psychological health in Rheumatoid Arthritis (RA). However, most people living with RA are insufficiently active to accrue health benefits. Interventions are therefore required to support physical activity (PA) behaviour change in this population.

Using theory to develop interventions, can inform what may be the strategies undergirding behavioural change, and provide a framework for testing the efficacy of the theory post-intervention in terms of hypothesised mechanisms. Self-determination theory (SDT) suggests that social environments which foster autonomous motivation toward a behaviour (i.e., intrinsic and personally identified reasons), will promote better uptake and maintenance of the behaviour. This study reports the theoretical process evaluation of an SDT-based exercise intervention for people with RA, which aimed to increase MVPA engagement and optimise psychological well-being.

Methods: Patients with RA (n = 115) were randomised to an SDT-based psychological intervention + RA exercise programme (experimental group, n=59), or a RA exercise programme only (control group, n = 56), delivered over 3-months. The SDT-based psychological intervention involved one-on-one consultations with a PA advisor, trained in strategies to promote autonomous motivation for PA (Table 1). Validated questionnaires assessed autonomous and controlled motivation for PA (Behavioural Regulation in Exercise Questionnaire-2), psychological well-being (Subjective Vitality Scale), and daily MVPA (International Physical Activity Questionnaire). Assessments were conducted at baseline (T1) and the end of the exercise programme (T2). Path analyses examined the hypothesised theoretical process model (Figure 1).

Results: Participants were excluded from analyses due to missing baseline data (n = 36), or as extreme outliers (n = 6). The hypothesised model (n = 73), demonstrated an excellent fit to the data [X² (26) = 34.10, p =.13, CFI = .96, RMSEA = .07]. The intervention promoted higher autonomous motivation and lower controlled motivation for PA at T2. In turn, changes in autonomous motivation from T1 to T2, significantly positively predicted changes from T1 to T2 in MVPA and subjective vitality. Controlled motivation did not significantly predict either outcome.

Conclusion: An SDT-based psychological intervention providing support for PA, may promote MVPA and more optimal psychological functioning in RA patients who are engaged in a tailored exercise programme.