What is the primary function of the serratus posterior inferior muscle?

The primary function of the serratus posterior inferior muscle is to assist in the depression of the ribs. This muscle is located at the back of the ribcage and plays a crucial role in respiratory mechanics, particularly aiding in forced expiration. When this muscle contracts, it pulls the lower ribs downward, which decreases the volume of the thoracic cavity and assists in expelling air from the lungs during activities such as coughing or during heavy exertion when more airflow is needed.

Understanding this muscle’s role emphasizes the importance of rib movement in respiratory functions and highlights its contribution to posture and movement stability in the thoracic region. While other muscles are involved in rib elevation during inhalation, the serratus posterior inferior is specifically adapted to facilitate rib depression.