The subscapularis muscle medially rotates and depresses the head of the humerus.  The subscap not only depresses the head of the humerus but also pulls it posteriorly, thus offsetting the muscles acting to cause anterior/superior glide of the humerus.  The subscap and the joint capsule together provide anterior glenohumeral stability.

Actions

• Medially rotates the shoulder (glenohumeral joint)
• Stabilizes the head of the humerus in the glenoid cavity

Origin

• Subscapular fossa of the scapula

Insertion

• Lesser tubercle of the humerus

Nerve Innervation

• Scapular