accessory muscle use

Accessory muscle use is the visible recruitment of muscles in the neck, shoulders and chest wall to help with breathing when the usual effort is no longer enough. In calm breathing the diaphragm does almost all the work quietly; calling in these backup muscles is a clear outward sign that breathing has become hard labor.

The muscles most often seen are the sternocleidomastoids running down the sides of the neck and the scalenes, which lift the upper rib cage and visibly tense and stand out with each breath. Patients in distress often brace their arms on a table or their knees, fixing the shoulder girdle so these muscles can pull harder on the chest. Drawing-in of the spaces between and above the ribs, called retractions, is a related sign especially obvious in children.

This pattern accompanies severe asthma, COPD exacerbations, pneumonia and any cause of respiratory distress. It is a powerful clinical sign precisely because it does not require any equipment: a clinician can recognize a patient working hard to breathe across the room. Persistent, escalating accessory muscle use, especially if the patient tires and the effort falls off, can warn of impending respiratory failure.