Abstract Exercise is one of the most promising methods for positively influencing neurocognitive function in late adulthood. Yet, despite this recognition, several major knowledge gaps preclude the ability to broadly prescribe exercise to prevent or treat cognitive impairment. This R35 proposal includes a series of innovative and potentially groundbreaking studies that will contribute to major advancements in the field of exercise and brain health. The studies that we describe in this proposal would be led by several highly promising junior scientists with the support of an experienced and dedicated mentorship team. The conceptual and scientific framework for the hypotheses described in this proposal orbit around three major challenges facing the field of exercise and cognitive aging: (1) We have a poor understanding of the mechanisms by which exercise influences cognitive function in late adulthood, (2) We have a poor understanding of the factors that moderate, or explain individual variation in, the response to exercise, and (3) We do not understand the factors that predict long- term adoption of exercise behavior and how to reduce barriers and enhance incentives for individuals who find it challenging to continue to exercise. Despite the clear benefits of an active lifestyle, most people fail to meet public health recommendations for exercise. The more we know about the factors that predict and enhance long-term adoption of exercise, the more we will know about whether exercise influences incidence of Alzheimer’s Disease and best practices for prescribing and maintaining exercise for the prevention and treatment of cognitive impairment. We propose to conduct secondary analysis of banked data from two rigorous and well-controlled supervised exercise randomized clinical trials (RCTs) and to conduct a 3-year follow-up of >570 participants from both of these RCTs of exercise to assess cognitive, cardiorespiratory fitness, and physical activity levels. In particular, we propose to examine whether exercise-induced changes in cardiometabolic and sleep measures mediate exercise-derived benefits to cognitive and brain outcomes. We will also target moderators of exercise including APOE genotype and racial disparities to better characterize which individual difference variables influence the magnitude of effects of exercise on brain health. Finally, we propose a discovery aim that would leverage our rich measurement of participants at the genetic, physiological, brain, cognitive, and socioemotional levels to perform predictive modeling to forecast long-term adoption of exercise (or barriers prohibiting long-term adoption). In short, this research proposal describes a broad and ambitious line of work that will produce groundbreaking and innovative studies to address significant gaps in our understanding of exercise and brain health in late adulthood. The aims target several major AD/ADRD milestones identified by NIH and will position junior scientists in ...