PROJECT SUMMARY/ABSTRACT The older cancer survivor is particularly affected by cancer and its treatments with numerous physical, mental, and psychosocial short- and long-term side effects, such as an increase in risk to experience chronic pain symptoms. Strong evidence indicates physical activity is correlated with lower rated symptoms of chronic pain. Despite the known benefits of physical activity, only 7% of older cancer survivors meet current physical activity recommendations. High ratings of pain are associated with low physical activity levels in older cancer survivors. Therefore, it is critical to understand how and when to best deliver physical activity intervention health messaging to reduce chronic pain symptoms among older cancer survivors who experience chronic pain symptoms. This application proposes the career development plan for Dr. Whitney Welch to establish an independent research program examining the relationship between physical activity and the maintenance of independence through the reduction of chronic symptoms among older cancer survivors. Dr. Welch's career development will be supported by an exceptional interdisciplinary group of investigators with a lengthy history of federal funding and a track record of successful mentorships. Her mentors, Dr. Rini, Dr. Spring, and Dr. Wolf are internationally recognized scholars in the areas of cancer survivorship, adaptive intervention design, and health literacy and health communications, respectively. The overall aim of this application is to develop and test the timing of physical activity promotion messages to increase physical activity and reduce pain symptoms among older cancer survivors who experience chronic pain symptoms using a micro-randomized trial design. In Aim 1, we propose to use a patient-centered, health literacy approach to develop and select theory-based health messaging that increase survivors' likelihood of engaging in physical activity tailored to their current pain symptoms. In Aim 2, we will conduct a micro-randomized trial, a new experimental design developed to optimize the construction of in-the-moment interventions, to determine the optimal pain state (pain/no pain) to deliver a message to increase physical activity and the probability that older cancer survivors will engage in physical activity. Finally, we propose an exploratory aim to determine the optimal pain state (pain/no pain) to deliver the message to increase physical activity and the probability participants will experience a subsequent pain episode. Results from this study will provide a robust foundation for a R01 submission to conduct a just-in- time adaptive physical activity intervention to manage pain symptoms in older cancer survivors. This award will directly lead to the establishment of an independent research program in physical activity and health research among older cancer survivors.