Question
Are accessory muscles used?
Answer
Yes. During increased breathing effort, people can recruit accessory respiratory muscles such as the sternocleidomastoids, scalenes, and intercostals; quiet breathing normally relies mainly on the diaphragm and intercostal muscles. Visible accessory-muscle use is a sign of respiratory difficulty and should be considered alongside signs such as rapid breathing, cyanosis, retractions, or paradoxical breathing.
Source: MSD Manual Professional Edition: Evaluation of the Patient With Pulmonary Issues (last updated October 2025).