Wearable-Measured Physical Activity Goal Adherence and Body Composition Change in a 12-Month mHealth Weight Loss Trial.

BACKGROUND: Wearable activity trackers are commonly used in mHealth weight loss interventions, but evidence linking adherence to moderate-to-vigorous physical activity (MVPA) goals with changes in body composition is limited. We examined associations between adherence to study-prescribed MVPA goals and changes in percent body fat and sex-specific waist circumference (WC) over 12 months in the SMARTER trial. METHODS: Participants (N = 502, 79.5% female; mean age 45 years; mean BMI 33.7 kg/m 2 ) were randomized to self-monitoring of diet, PA, and weight (SM) or SM plus daily tailored feedback messages (SM + FB). Weekly adherence to ≥300 min/week of MVPA was quantified using Fitbit-derived equivalents. Associations between MVPA adherence and changes in percent body fat and sex-specific WC over 12 months were examined using linear mixed models. RESULTS: Among the full sample, greater MVPA adherence was associated with reductions in body fat (b = -0.01; 95% CI: -0.02, -0.005), but not in WC (women: b = -0.01; -0.03, 0.01; men: b = -0.03; -0.05, 0.0002). Among the completers, higher adherence was associated with decreases in body fat (b = -0.01; -0.02, -0.004) and WC (women: b = -0.02; -0.04, -0.004; men: b = -0.04; -0.08, -0.003). CONCLUSIONS: Higher MVPA adherence was associated with favorable changes in adiposity over 12 months, supporting the use of wearable-derived PA measures in long-term mHealth behavioral interventions.