Trajectories of Adherence to Study-Prescribed Physical Activity Goals in a mHealth Weight Loss Intervention

Introduction: Engaging in ≥300 min/week of moderate-to-vigorous physical activity (MVPA) is recommended for weight management. This study identified MVPA goal-adherence trajectories and associated predictors and weight outcomes in a 12-month mHealth weight-loss trial. Materials and Methods: This was a secondary analysis of valid PA data (≥4 days/week with ≥500 steps/day) from participants (age ≥ 18 years, BMI 27-43 kg/m²) randomized 1:1 to self-monitoring with tailored feedback or self-monitoring only. Both groups received Fitbit trackers. Group-based trajectory modeling identified adherence trajectories and baseline predictors. Analysis of variance was used to estimate associations between trajectory group membership and 12-month weight change. Results: Among 502 participants (79% female, 82% White, mean age of 45.0 ±14.4 years), four MVPA goal-adherence trajectories were identified: lower stable (34.5%), moderate (39.8%), increasing (19.3%), and high (6.4%). A graded association was observed with better adherence trajectories being associated with greater 12-month weight loss (p < 0.0001). Older age, male sex, being unpartnered, and higher first-week MVPA predicted membership in higher adherence trajectory groups (p < 0.05). Conclusions: Higher MVPA goal-adherence was related to greater weight loss. Early MVPA levels predicted long-term adherence, supporting the importance of personalized, technology-supported strategies to promote long-term PA adherence and inform targeted interventions to prevent chronic diseases.