Serratus Anterior

The serratus anterior runs from the upper ribs to the medial border of the scapula, wrapping around the side of the rib cage. Its main job is protraction of the scapula (drawing the shoulder blade forward, away from the spine) and assisting upward rotation of the scapula so the arm can be raised overhead. Because it anchors the scapula against the rib cage, it appears throughout the source's exercise tables as a secondary (assisting/stabilizing) muscle rather than a prime mover — most often in pressing and overhead movements.

In the source it is labeled on the posterior upper-back diagram alongside the trapezius and rhomboids, and it is listed as a secondary muscle in exercises such as the bench press, incline press, military/overhead press, push-up, and several other pressing movements.

• Action: scapular protraction; assists upward rotation of the scapula.
• Location: lateral rib cage, attaching to the medial border of the scapula.
• Role: predominantly a stabilizer / secondary muscle in pressing and overhead work.

• scapular-movement — protraction is one of the scapular movements it drives.
• trapezius, rhomboids — antagonist/partner scapular muscles (retraction vs protraction).
• bench-press, military-press, push-up — exercises that recruit it as a secondary muscle.