Preparing to optimize a multimodal adaptive intervention for physical activity behavior change among middle age and older adults - PROJECT SUMMARY / ABSTRACT Dr. Allyson Tabaczynski is applying to the F32 Kirschstein-NRSA Postdoctoral Fellowship for the necessary training to build a career committed to developing effective, scalable interventions targeting sustained physical activity behavior change for middle-aged and older adults. Physical activity across the lifespan is critical for healthy aging. Yet very few US adults are meeting the recommended guidelines, and participation further declines with age. Behavioral interventions often elicit heterogeneous responses because they fail to engage targeted mechanisms of adherence to behavior change. Multimodal adaptive interventions, utilizing digital and human components, can offer a scalable person-centered approach for creating more consistent behavior change. The candidate’s primary mentor, Dr. David Conroy, has developed Precision AIM, a just-in-time adaptive intervention that sends text messages to promote physical activity using a highly individualized approach. Dr. Tabaczynski seeks to expand this digital intervention into a multimodal adaptive intervention to maximize the potential for a positive intervention effect across all middle age and older adults. This proposal describes the preparatory phase of research that will be conducted during the F32 fellowship to inform the design of this future multimodal adaptive intervention. Aim 1 involves statistical modelling of baseline demographic and motivational characteristics, changes in step counts during the intervention, and seasonal factors to determine early predictors of intervention response to the Precision AIM digital intervention. Aim 2 will use mixed methods (i.e., secondary statistical analysis and a follow up interview) to compare changes in psychological mechanisms of behavior change between responders and non-responders. Results will dictate (1) when the digital intervention will be stepped up to include human-delivered support for to those who need it, and (2) what mechanisms of behavior change should be targeted in the stepped-up supports for an optimal effect on physical activity participation and mechanisms of adherence. This research and the planned training activities will advance the candidate’s knowledge and skills for (1) understanding age-related determinants of sustained behavior change, (2) using complex statistical analyses and mixed methods to understand individual differences in physical activity behavior and intervention response to a greater depth, (3) optimizing adaptive interventions, and (4) further professional development. This proposal presents a clear, strategic pathway to advance Dr. Tabaczynski’s training and achieve their goal of an independent research career.