Multiphase Optimization Strategy (MOST) methodology will be used to determine which intervention components or component combinations optimally increase daily steps in a 12-week intervention with a 12-week follow-up. MOST is a framework adapted from engineering that uses highly efficient factorial experiments to evaluate individual, and combined, effects of intervention components to determine which ones can be reduced, eliminated, or replaced to improve efficiency. Insufficiently active people with metastatic breast cancer (MBC) will receive a core intervention consisting of the FIt2ThriveMB app and Fitbit and be randomly assigned to four components, each with two-levels, under consideration for inclusion in the optimized intervention: 1) EHR-integration (on v. off); 2) coaching dose (weekly v. bi-weekly; 3) social+ (on v. off) and 4) goal-setting type (highly tailored v. static). The effects of increasing PA on symptom burden, other intensity activities (i.e. moderate to vigorous, light and sedentary), and functional performance and potential mediators and moderators of component effects will also be examined. Knowledge gained from this study will inform the development of more effective and scalable interventions to improve health and disease outcomes in this population.
