Abstract 13075: Initial Physical Activity Level is a Strong Predictor of Adherence to the Physical Activity Goal: A Secondary Analysis of the SMARTER Weight Loss Trial

Abstract

Background: Over a third of excess coronary heart disease mortality in the US is related to inadequate physical activity (PA). Use of wearable activity trackers is beneficial for PA improvement in many populations. However, predictors of long-term adherence to PA remain unknown. Hypothesis: The 1 st week PA levels will be the strongest predictors of long-term adherence to the PA goal in adults with overweight or obesity in a mHealth weight loss intervention trial. Methods: A secondary analysis of a 12-month behavioral weight loss trial (SMARTER) that randomized 502 participants to either self-monitoring with tailored feedback messages (SM+FB, n=251) or self-monitoring alone (SM, n=251) was conducted. At baseline, each participant received a Fitbit Charge 2 and PA goal of ≥150 minutes of moderate or vigorous activity (MVPA) per week. The outcome of interest for this analysis was long-term PA adherence, i.e., the number of weeks adherent to PA goal over 12 months. Twenty-six explanatory variables were considered, including treatment assignment; baseline socio-demographics; health history; body mass index (<30 vs. ≥30 kg/m 2 ); psychosocial factors; and1 st week PA levels (<150 vs. ≥150 MVPA min/week). Machine learning methods (i.e., random forest regression trees and lasso regression) were used to identify predictors of long-term PA adherence. Results: The sample ranged in age from 19 to 75 years (57% were <50 years old), and was mostly Caucasian (83%), female (80%) and had a mean BMI 33.7 ± 4.0 kg/m 2 . The sample was randomly split 4:1 into training (n=394) and validation subsamples (n=104) which were comparable by treatment assignment. Both random forest and lasso regression identified 1 st week PA levels as the most important predictor of long-term PA adherence. The findings were confirmed in the validation cohort with an out-of-sample R-square of 40.2% from random forest and a R-square of 47.9% from lasso regression, suggesting good predictive abilities. Conclusion: This analysis confirmed higher initial PA levels as the strongest predictor of long-term PA adherence. The findings support screening for PA at study entry and developing tailored interventions for those with lower initial PA levels.