INTRODUCTION: Patients with a metastatic breast cancer suffer from a deteriorated quality of life and numerous symptoms such as pain, severe fatigue and a decrease of their physical fitness. As the feasibility of a physical activity program has been demonstrated in this population, ABLE02 aims to assess the efficacy of a 6 month-physical activity program based on connected devices to improve health-related quality of life and to reduce fatigue in women with metastatic breast cancer. METHODS/ANALYSIS: ABLE02 is a prospective, multicenter, randomized, controlled and, open-label study. 244 patients with a metastatic breast cancer , at least one positive hormone receptor and a first-line chemotherapy planned will be randomly assigned (1:1 ratio) to: (i) the intervention arm to receive physical activity recommendations, an activity tracker to wear 24 hours a day during the whole intervention (6 months) with at least three walking sessions weekly and quizzes to answer each week on physical activity and nutrition (ii) the control arm to receive physical activity recommendations only. Assessments will be conducted at baseline, M3, M6, M12 and M18 to evaluate the clinical, physical, biological and psychological parameters and survival of participants. All questionnaires will be completed on a dedicated application. DISCUSSION: An activity program based on smartphone application linked to an activity tracker may help to improve quality of life and reduce fatigue of patients with a metastatic breast cancer. The growth of e-health offers the opportunity to get real-time data as well as improving patient empowerment in order to change long-term behaviors.