Subscapularis

backMusculus subscapularis

The subscapularis is the only rotator cuff muscle on the front of the shoulder blade — it fills the whole surface facing your ribs — and it is the one that rotates your arm inward.

The subscapularis is sandwiched between the shoulder blade and the ribcage, filling the entire front surface of the bone. Its fibres converge outward into a tendon that passes in front of the shoulder joint and attaches to a bump on the front of the arm bone. Because it is trapped between two other structures, it is the only rotator cuff muscle you cannot touch from anywhere.

It is also the only one that rotates the arm inward. The other three rotate outward or lift; the subscapularis pulls the opposite way, which is what balances the group. In a shoulder that works well, front and back of the cuff are pulling against each other continuously and the arm bone stays centred as a result.

Its stabilising role is specific and important: it is the main thing at the front of the joint resisting the head of the arm bone sliding forward. That matters most when the arm is out to the side and rotated back — the position at the bottom of a bench press, or a throwing arm cocked to throw — where the joint is at its most open.

It is generally described as the largest and strongest of the four cuff muscles, and it is by some way the least discussed of them, mostly because it is invisible and difficult to reach.

Training notes

Internal rotation with a band or cable, elbow tucked at the side, forearm sweeping in toward the stomach, is the direct movement. It gets prescribed far less often than external rotation, and for a defensible reason: internal rotation is already trained by every press, every pulldown and every row, since the pecs and lats do it too.

That said, the subscapularis is not the same as the pecs and lats, and it does the front-of-joint stabilising work that they do not. A light set or two of internal rotation alongside external rotation costs nothing and keeps the pairing balanced.

What is worth avoiding is the common assumption that because internal rotation is well trained by pressing, the subscapularis is well trained by pressing. In a press, it is holding the joint together rather than moving it — the same distinction that applies to the whole cuff.

Anatomy

Origin
  • Subscapular fossa, on the costal surface of the scapula
Insertion
  • Lesser tubercle of the humerus
Actions
  • Internally rotates the humerus, turning the arm inward
  • Holds the head of the humerus in the socket and resists it sliding forward
  • Assists adduction and extension of the arm
Innervation
Upper and lower subscapular nerves (C5–C6)

Exercises

Antagonists

Synergists