The rotator cuff is four small muscles whose job is to hold the ball of the shoulder centred in its socket while the big muscles move the arm. They are often described as the guardians of the shoulder joint, and when they stop doing that job well, the tendons get pinched in the narrow space above.
The painful arc
The characteristic sign is a band of pain partway up. Lifting the arm out to the side is comfortable at first, hurts through the middle range, then often eases again near the top. That is the tendon being compressed as it passes through the tightest part of its travel.
What usually causes it
- Overhead volume — throwing, swimming, pressing, racket sports, or a weekend of decorating.
- Poor shoulder blade control, so the space the tendons run through does not open as the arm lifts.
- Rounded posture, which narrows that space before you have even moved.
- A stiff mid-back, forcing the shoulder to make up the difference.
What treatment involves
Releasing what is restricting the movement, settling the irritated tissue, and restoring the shoulder blade mechanics that create space for the tendon.
Then strengthening — specifically the cuff and the muscles controlling the shoulder blade. This is a control problem more than a tissue problem, and strengthening is what makes the improvement stick.