Short and long-term effects of a self-determination theory-based physical activity intervention on basic...

The aims of this study were to investigate the short and long-term effects of a physical activity intervention on basic psychological needs (BPN); and to examine whether autonomy, competence, and relatedness mediated the relationship between the intervention and depressive symptoms in adults. A 16-week randomized controlled trial was conducted, combining online and in-person activities. The intervention involved two weekly sessions, each lasting 90 min, comprising theoretical (44 %) and practical (56 %) components designed to promote physical activity (PA). Each session employed strategies aimed at satisfying BPN (autonomy, competence, and relatedness) to support behavior change. BPN and depressive symptoms were assessed using validated questionnaires at baseline, post-intervention, and at a 6-month follow-up. Generalized estimating equations were applied for both per-protocol (PP) and intention-to-treat (ITT) analyses, while structural equation modeling was conducted using ITT data only. A total of 78 individuals participated, equally allocated to either an intervention group (IG) or a control group (CG), with comparable distributions of sex, age, and severity of depressive symptoms at baseline. Significant group-by-time interactions were observed for autonomy (η²p = 0.031; p = 0.086), competence (η²p = 0.047; p = 0.100), and relatedness (η²p = 0.099; p = 0.017) in the PP analysis, favoring the IG, particularly at post-intervention. Additionally, ITT analysis revealed that both the overall needs score and the autonomy, competence, and relatedness subscales mediated the relationship between the treatment and depressive symptoms, considering the difference between post-intervention and baseline values. Although the intervention did not significantly improve BPN in the ITT analysis, these needs functioned as mediators, contributing to the reduction of depressive symptoms in adults with elevated symptomatology. TRIAL REGISTRATION: Brazilian Registry of Clinical Trials (ReBEC): RBR-7466htj, April 17, 2023. Retrospectively registered.