Serratus Anterior

The Serratus Anterior forms the lateral aspect of the upper torso musculature. It originates on the ribcage, attached to all but the lowest of the full ribs (numbers 1-9), and inserts at the medial anterior edge of the scapula. The tendon attachments on each rib, give the muscle an appearance similar to the edge of a serrated knife, which is where the name SERRATUS comes from. The “fingers” of the serratus anterior interlace with the “fingers” of the external oblique muscles and share fascial attachments on the ribs. Only a portion of the muscle can be seen. The pectoralis major lays over the upper portion of the SA, but the inferior four or five heads can be visible on lean people.

Shown here, it looks like a row of bumps on the torso wall, just below the armpit.


The actions of the serratus anterior are to pull the scapula away from the midline and to pull it closer into the ribs, hugging the body. It also functions to stabilize the scapula during contractions of the pectoralis major. A weakness or failure to engage the serratus anterior will allow the scapula’s inner border to “wing out” which is when the interior border of the flat bone lifts away from the rib cage and visibly pokes up off the back causing the flesh to tent.
The antagonist muscles are the rhomboid and trapezius, which pull the scapulae back towards the midline. In fact, the rhomboids share the fascial attachment to the scapula and pull in a kind of tug-of-war with the Serratus Anterior.

If this muscle goes into spasm it can cause a feeling similar to having a heart attack or lung cancer. The best way to stretch the SA is to contract your rhomboids while abducting and flexing your gleno-humeral joint.