Diaphragm's Role as a Systems-Connector Muscle: A Narrative Review

The diaphragm muscle (DM) is the most complex muscle in the entire musculoskeletal system, and it is associated with the most systemic actions. It is often labeled a pump, reflecting its role in the respiratory and circulatory systems. In reality, the DM's functions are broader, and the term "pump" does not adequately capture its importance. Clinically, DM is rarely considered to improve movement, cognitive and emotional functioning, or its influence on the immune response. Clinically and based on two-dimensional instrumental examinations, it is believed that DM "flattens" during inspiration or in the presence of chronic obstructive pulmonary disease (COPD). In contrast, we highlight, based on literature employing three-dimensional clinical instrumentation, that DM does not change its morphology during inflation. Therefore, the importance of DM functional assessment lies not in its shape but in its ability to move. To conclude, we propose a hypothesis for an adjective that best reflects the systemic functional complexity of DM.