Pulmonary Rehabilitation (PR) is an evidence-based intervention to effectively manage the physiological and psychological effects of Chronic Obstructive Pulmonary Disease (COPD). The aims of PR are to improve symptoms of COPD, increase exercise capacity, increase independency, improve overall behaviour related to health (like exercising more), and enhance quality of life. The cornerstone of PR programmes is aerobic exercise prescription. Typically, walking exercise is used, and the prescription is individualised for each patient based on their maximal walking exercise capacity. However, adherence to walking exercise is challenging for service users, particularly when unsupervised at home. The use of music during exercise shows promise as a tool to decrease the perception of fatigue and increase motivation, but the integration of music via smartphone applications to support walking exercise adherence during PR has not been explored. This project aims to assess if a new mobile application BeatClearWalker (BCW) intervention is practical, acceptable, and effectively used by people living with COPD. The app is designed to help people living with COPD attending PR adhere to their prescribed walking pace during exercise. The BCW app provides real-time, personalised music feedback through music degradation to optimise the dose of walking exercise.