The Rotator Cuff: Stability First

Four small muscles, one big job

The rotator cuff is a group of four deep muscles that wrap around the shoulder joint. A helpful memory aid is SITS:

• Supraspinatus — helps start lifting the arm to the side (abduction).
• Infraspinatus — rotates the arm outward (external rotation).
• Teres minor — also rotates the arm outward.
• Subscapularis — rotates the arm inward (internal rotation).

Stability first

The cuff's most important role is not producing big movements — it is keeping the ball of the humerus centered in its shallow socket. When the deltoid lifts the arm, the cuff pulls the humeral head down and in so the joint stays stable. Think of the cuff as the shoulder's steering and suspension, not its engine.

Why external rotation gets extra attention

Many everyday and gym movements (pressing, pushing) involve internal rotation. To keep the shoulder balanced, trainers often include gentle external-rotation work (like band external rotations) for the infraspinatus and teres minor. This is about balance and joint health, so light loads and good control matter more than heavy weight.

A commonly confused pair

Teres minor is part of the cuff and rotates the arm outward. Teres major (a different muscle) is not part of the cuff and rotates the arm inward. Same neighborhood, opposite rotation — a classic mix-up.