PROJECT SUMMARY Chronic pain (CP), a highly prevalent, costly, and disabling biopsychosocial condition, is being increasingly addressed with cognitive behavioral interventions such as Acceptance and Commitment Therapy (ACT) and Cognitive Behavioral Therapy (CBT). Such interventions seek to maximize physical, social, and occupational functioning by changing how one manages pain via addressing pain-related thoughts, beliefs, and behaviors. The current CP literature is limited by the use of between-subject designs and self-report measures that lack ecological validity and may be subject to bias. One component of function, physical activity, is able to be objectively measured in an ecologically valid way using accelerometry. In fact, prior research has combined accelerometry and pain ratings collected using ecological momentary assessment (EMA) to better reflect the real-time, real-world relationship between pain and physical activity. Such research has indicated cross- sectionally a dynamic within-person pain-physical activity relationship. We hypothesize that this dynamic relationship is alterable by cognitive behavioral intervention and seek to examine this research question in Veterans with CP, as they represent an underserved and apt population for CP research given disproportionately high rates of this condition. In Aim 1, we model the relationship between EMA-assessed pain and objective physical activity over a 7-day baseline period, within-person, using parallel latent growth curve modelling (LGCM). We hypothesize that at baseline, the growth trajectories of pain and physical activity will be related such that increases in pain will be associated with decreases in physical activity. In Aim 2, we use multigroup analysis to examine if participation in a cognitive behavioral intervention alters the relationship between the growth trajectories of EMA pain and objective physical activity. We hypothesize that, post- intervention, the relationship between the growth trajectories of pain and physical activity will be significantly altered compared to baseline. In our Exploratory Aim, we conduct follow-up interviews to qualitatively explore how treatment impacts how individuals relate to their pain. Therefore, the proposed research will examine the relationship between pain and physical activity and if and how it changes after cognitive behavioral intervention. The use of structural equation modelling (i.e., LGCM) and qualitative methods will be combined to portray a more complete picture of the experience of CP and treatment. Thus, findings from this study will address existing limitations in the understanding and conceptualization of function in CP, provide information on how to improve function in individuals with CP, and promote the improvement and refinement of cognitive behavioral interventions for the treatment of CP. Importantly, this project will advance the applicant’s long-term goal of becoming an independent clinical researcher committed t...