Inclusion Criteria:  meet the National Institute for Health and Care Excellence Osteoarthritis (NICE) clinical criteria:  being at least 45 years of age; having activity-related joint pain; having morning stiffness ≤ 30 minutes; have a history of knee pain for at least 12 weeks; are interested in becoming more physically active; have either a cell phone or laptop/desktop computer with broadband internet connection and working email address; and are able to commit to the study for 12 weeks and willing to wear physical activity monitors live in the contiguous United States comfortable participating in a program delivered in English is able to safely participate in a moderate-intensity exercise as determined by a pre-exercise screen questionnaire.  Exclusion Criteria:  regularly exercise more than 60 minutes/week; or has a scheduled knee or hip joint replacement; or has had physical therapy for knee OA in the past 6 months; or participated in a strength training program for the lower extremities in the past 6 months.