Although evidence in favor of physical activity (PA) for reducing age-related cognitive decline and associated Alzheimer’s risk continues to grow, critical issues are persistently low PA adoption and adherence during critical periods for Alzheimer’s prevention. Because PA starts declining at middle-age and neurodegenerative pathologies increasing Alzheimer’s risk start decades before cognitive impairment, there is a pressing need to understand how and why middle-age adults can more successfully adopt and sustain PA. Self-regulatory capacities have been identified as critical for acting on our intentions and plans to be more physically active, however causal evidence testing whether and how strongly self-regulatory capacities affect PA behavior change is absent from the literature. Therefore, our objective is to test the causal role of the self-regulation construct, cognitive control, in PA behavior change among inactive middle-aged adults. Based on the Temporal Self-Regulation Theory (TST), we hypothesize cognitive training designed to improve cognitive control will increase the success of a PA behavior change program, and training cognitive control with emotionally valenced stimuli will further increase moderate-to-vigorous PA adherence. Our predictions are based on research showing the importance of cognitive control in PA adherence and maintenance, evidence that negative affective experiences of PA are common and detrimental to future PA, and the modifiability of cognitive control with adaptive cognitive training. We test our overall hypothesis with three aims, including an R61 phase (Aim 1) to develop and refine a computerized training program targeting aspects of motivation, planning, and cognitive control theorized to promote PA behavior change, followed by an implementation R33 phase (Aim 2) with a lab-based, randomized controlled trial (RCT) to determine the extent that cognitive control for emotionally valenced information is a target mechanism for PA behavior change in inactive middle-age adults at moderate-to-high risk for Alzheimer’s. The RCT implemented in Aim 2 will be tested across rural and urban sites to increase diversity and generalizability of our sample, which forms the basis for (Aim 3) determining moderators of intervention efficacy for improving PA behavior change. We predict those with poor cognitive control and high negative affective experiences to moderate intensity PA will benefit most from cognitive control training targeted to an affective domain for PA behavior change. Our results will be significant by determining the causal role of cognitive control and affect in sustainable PA behavior change in midlife, a critical prevention period for Alzheimer’s. Success will culminate in a scalable training program to boost PA adherence, setting the stage for personalized and accessible strategies for midlife adults to change their course towards a more physically active lifestyle and a virtuous cycle of sustained cognitive ...