The diaphragm is the main muscle of breathing. Itâs supposed to do most of the work. When you have COPD, the diaphragm doesnât work as well and muscles in the neck, shoulders and back are used. These muscles donât do much to move your air. Training your diaphragm to take over more âwork of breathingâ can help. Diaphragmatic breathing is not as easy to do as pursed-lips breathing.