PROJECT SUMMARY HAIL ABSTRACT Older adults (age ≥ 60 years) tend to be less physically active than younger adults, engaging in less than 11% of recommended physical activity (PA) levels. Lack of PA in older adults is associated with increased risk of all-cause mortality. Large population-based studies suggest that moderate levels of PA provide protection from chronic diseases in older adults. Therefore, interventions aimed at improving PA in older adults could significantly improve health outcomes. To increase PA in older adults, we use the socioecological perspective to examine the barriers and facilitators at each level of influence (i.e., intrapersonal, interpersonal, organizational/community, environmental/policy). A PA intervention developed for older adults that targets multiple levels of the socioecological model is needed. The evidence-based Fit and Strong! (F&S!) program for older adults, funded by the National Institute of Aging, can be optimized to bypass these barriers and effectively engaged older adults in sustained PA. Although the F&S! program has been successfully implemented in multiple community-based settings, it is limited because it is only offered in-person (i.e., no online component) and ends at 8 weeks with very little ongoing support. These limitations not only increase the cost and reduce the accessibility of the program but also fail to optimize or support gains made as improvements in PA during F&S! diminish over the follow-up phase. We will bypass these limitations and develop an adjunct, online platform to the F&S! program that is capable of syncing with wearable devices (e.g., fitbit). To create this platform as well as examine its feasibility and acceptability, we will administer the program in churches and senior centers in Boston, MA. Consistent with this FOA “to provide support for up to two years (R21 phase) for research planning activities and feasibility studies” we will conduct: 1) focus groups at two sites to better understand the key barriers necessary to bypass at every level of the socioecological model and then build this adjunct, online program to create the F&S!-Online program and 2) an open pilot study (N=30) across these two sites to examine the feasibility and acceptability of the F&S!-Online program. Per the FOA, the R21 will be, “followed by a possible transition to expanded research support (R33 phase) for optimizing the intervention and conducting larger-scale feasibility studies”. Consistently, for the R33 phase, we will conduct a larger scale feasibility study by randomizing sites to either F&S!-Online or the standard F&S! (N=120) to determine the feasibility and acceptability of the online adjunct platform as well as pilot its efficacy and sustainability.