The muscles of respiration are those muscles that contribute to inhalation and exhalation, by aiding in the expansion and contraction of the thoracic cavity. The diaphragm and, the intercostals muscles drive respiration during quiet breathing. Maintenance of the elasticity of these muscles is crucial to the health of the respiratory system and to maximize its functional capabilities.

Diaphragm

The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so that its center moves caudally (downward) and its edges move rostrally (upward). This compresses the abdominal cavity, raises the ribs upward and outward and thus expands the thoracic cavity. This expansion draws air into the lungs. When the diaphragm relaxes, elastic recoil of the thoracic wall causes the thoracic cavity to contract, forcing air out of the lungs.

Intercostals muscles

Along with the diaphragm, the intercostals muscles are one of the most important groups of respiratory muscles. These muscles are attached between the ribs and are important in manipulating the width of the rib cage. There are three layers of intercostals muscles. The external intercostals muscles are most important in respiration. These have fibers that are angled obliquely downward and forward from rib to rib. The contraction of these fibers raises each rib toward the rib above, with the overall effect of raising the rib cage, assisting in inhalation.