The main purpose of this project is to promote physical activity in patients with osteoarthritis. More specifically, this study aims to test the acceptability of an app to promote physical activity in the target population, and consequently the feasibility of such an approach. A mobile phone application - namely PIANISSIMO - will be developed specifically for this project. It aims to spread knowledge on the benefits of physical activity and collect data on how this knowledge can induce behavior changes toward a more physically active lifestyle. The intervention is delivered via the app, which will send daily notifications on physical activity and sedentary behavior, and ask the participants to set their weekly goal (i.e., daily steps). The app will also collect daily steps count and ask the participant to fill in questionnaire on pain once a week.