Because the US population is aging and obesity is rising dramatically, the epidemic of arthritis-associated disability and its associated costs will significantly worsen, largely due to the consequences of knee osteoarthritis (OA). Knee OA is already a major cause of work disability and work absenteeism/presenteeism, especially among obese and overweight employees. In addition, total knee replacement surgeries have increased by 161.5% among Medicare participants over the past 20 years and are expected to quadruple in the next 20 years. Increased physical activity can relieve the pain and activity limitations of individuals with knee OA, but this healthy lifestyle behavior has not been embraced by a substantial proportion of the employed population. The overarching goal of this program is to develop and disseminate an affordable, efficient, efficacious physical activity intervention that can assist large groups of employees with or at risk for knee OA to attain and maintain healthy physical activity behavior. MobilWise is a 12-week RCT pilot that will use data transmitted from an affordable accelerometer-based personal monitor (Fitbit Flex) via customized remote- coach interface to 1) allow a remote coach to view and collect physical activity data generated by the personal monitor, and 2) use that data to formulate and provide tailored behavioral support via mobile phone, ba sed on the supportive accountability model and using motivational interviewing. The MobilWise intervention will use the media communication mode preferred by the participant (text, voice call, or video chat) to attain and sustain healthy physical activity behavior in Blue Cross Blue Shield of Illinois employees with knee symptoms after previous completion of an in-person, intensive intervention (Joint ADventure). Six month follow-up measures are planned. Specific aims are to: 1) assess the feasibility of conducting a randomized controlled trial of the Mobil Wise intervention at this worksite, 2) estimate the effectiveness of the intervention to increase objectively-measured physical activity, 3) to develop/refine the customized remote coach-interface, dashboard, and coaching protocol, and 4) to examine the accuracy of the affordable personal monitor (Fitbit Flex) by comparing that output with data from the state-of-the-art GT3X+ accelerometer. This study leverages the combined clinical and technologic expertise of Northwestern's Arthritis Center Accelerometer Unit and its Center for Behavioral Intervention Technologies, in cooperation with the Fitbit technology team and the Blue Cross Blue Shield of Illinois Corporation. If successful, a multi-site randomized controlled trial/R01 proposal will follow to demonstrate the effectiveness/cost-effectiveness of the Mobil Wise intervention in larger worksite populations. Given the influence that BCBS has in shaping future health practices and the scalability/generalizability of the proposed intervention, this research could have a tremendous impact on improving symptoms and quality of life for those with early knee OA as well as preventing the work absenteeism/presenteeism, work disability, and increased healthcare costs associated with knee OA.