Project Summary/Abstract Adults with chronic musculoskeletal disease, such as knee osteoarthritis (OA) or back pain, are in urgent need of an effective intervention to reduce sedentary behaviors, such as excessive sitting. Historically, interventions have targeted physical activity via supervised exercise, but have largely ignored sedentary behaviors. Such sedentary behaviors impact health in ways that are independent of exercise, including increased risk of mortality, diabetes, and obesity. This is relevant to adults with chronic musculoskeletal disease who spend up to 3.5 hours/day more in sedentary behaviors than their healthy counterparts, and where intervention targeting sedentary behaviors has yet to be tested. However, before we can plan and implement a clinical trial, a critical gap in knowledge that must first be filled is how much sedentary behaviors need to be reduced to have clinically meaningful improvements in health. Surprisingly, there are no established standards to define excessive levels of sedentary behavior, nor recommendations for how much they should be reduced. Consequently, we are blind to what amount of sedentary behaviors should be targeted for change, and a clinical trial would be a waste of time and resources until we first establish this. To fill this gap, we propose to examine the relation of reduced sedentary behavior with clinically meaningful changes in pain, physical function, and Health Related Quality of Life (HRQoL) over 2 years in a large, diverse community-based cohort study currently in the field. The objective of this study is to use a state-of-the-art monitoring device, the activPAL, to evaluate sedentary behaviors within 1,500 adults from the Johnston County Health Study (JoCoHS). Our proposal will establish for the first time much-needed thresholds for targeting sedentary behaviors that will overcome current limitations in the field for designing and implementing effective clinical interventions that address excessive sedentary behaviors. We are specifically interested in understanding how sedentary behavior impacts common, yet costly, musculoskeletal outcomes such as pain, strength, physical function, and HRQoL. The results stemming from this proposal will provide essential data that is necessary for us to plan for a future clinical trial which would then broadly inform the wider scientific community of how to address sedentary behaviors in adults with chronic musculoskeletal disease.