Mechanisms of action in a physical activity counseling intervention for adults awaiting metabolic and bariatric surgery: A single-case experimental feasibility trial.

Research into theory-based interventions for promoting physical activity (PA) has progressed; however, evaluating mechanisms of action remains essential to ensure implementation fidelity, assess whether the intervention alters targeted constructs, identify what drives behavior change, diagnose intervention failure, optimize future interventions, and assess causal pathways posited by theory. Although theory-based interventions allow researchers to map out how their intervention will drive behavior change, empirical testing is required to support or refute the proposed mechanisms of action. Drawing on self-determination theory (SDT) and social cognitive theory (SCT), the TELEhealth BARIatric (TELE-BariACTIV) intervention aimed to influence PA-related behavioral regulations, basic psychological needs, enjoyment, self-efficacy to overcome barriers, and perceived social support to increase PA levels among adults awaiting metabolic and bariatric surgery. This study presents trends in targeted SDT and SCT components during a multicenter feasibility trial with a multiple-baseline single-case experimental design. Twelve adults (Mage = 52 ± 7 years; female = 92%; MBMI = 47 ± 6 kg/m2) enrolled, 11 received six 45-min, weekly videoconference PA counseling sessions. To ensure theoretical alignment, employed behavior change techniques were directly mapped to SDT and SCT components. Data collected at study entry, pre-intervention, and post-intervention were analyzed descriptively and graphically. When expressed as mean percentage change, favorable changes (>5%) were observed for: introjected regulation (-8%), intrinsic motivation (+9%), relatedness frustration (-7%), enjoyment (+8%), self-efficacy to overcome external barriers (+8%), and family/household member support (+6%). Graphing individual scores across timepoints revealed heterogeneity across participants. The findings will inform TELE-BariACTIV intervention refinement to achieve greater changes in the targeted theoretical components. A mechanistic study nested within a larger trial is planned to test hypotheses regarding mechanisms of action and explore factors associated with response heterogeneity.