App-Based Physical Activity Intervention for Individuals With Depression (MoodMover): Single-Arm, Pre-Post Proof-of-Concept and Feasibility Study.

Background: Depression is a prevalent mental disorder, and it remains one of the leading causes of disability in Canada and globally. Mobile app-based physical activity interventions may offer an effective and accessible treatment option for individuals with depression who cannot or prefer not to access supervised exercise programs. Objective: This study aims to investigate the feasibility, acceptability, and proof of concept of a 9-week, theory-guided, app-based physical activity promotion intervention (MoodMover) developed for people with depression. Methods: We conducted a single-arm, pre-post study from November 2024 to May 2025, following the phase IIa: Proof-of-concept and phase IIb: Pilot and Preliminary Testing of the Obesity-Related Behavioural Intervention Trials model. Physically inactive adults who either self-reported a diagnosis of major depressive disorder or reported at least mild depressive symptoms, operationalized as a minimum score of 5 on the Patient Health Questionnaire, 9-Item, were recruited. The intervention spanned 9 weeks, with the first week serving as a run-in period and including a 15-minute orientation session on the first day. Participants were instructed to use the MoodMover program, delivered via the Pathverse app. Feasibility was assessed based on 4 primary criteria: recruitment, adherence, usability, and retention. Proof-of-concept was evaluated by assessing changes in physical activity behavior and depressive symptoms over the intervention period. Results: From November 2024 to March 2025, 32 of the 51 adults who met eligibility criteria consented to participate in this study, resulting in a recruitment rate of 63%. Twenty-eight participants completed baseline assessments, with a mean age of 39.8 (SD 13.4) years. A total of 21 participants attended the orientation session and received the intervention. Retention, adherence, and usability rates were 57% (16/28), 67% (14/21), and 50% (8/16), respectively. Regression analyses found that age consistently associated with app engagement, usability, and satisfaction. Two-tailed paired t tests indicated significant pre-post changes in self-reported moderate to vigorous physical activity and depressive symptoms across the 75%, 85%, and 95% CIs. Among participants with clinically elevated depressive symptoms at baseline (Patient Health Questionnaire, 9-Item ≥10), 75% (9/12) achieved a clinically meaningful reduction in symptom severity. Conclusions: Our findings suggest that MoodMover holds potential for promoting physical activity behavior among individuals with depression and supporting depression management at scale. However, the feasibility of the tested version remains suboptimal. Necessary modifications (eg, improvements to enhance the accuracy of step tracking) should be implemented and reevaluated before progressing to a more rigorous efficacy trial.