The rotator cuff is a group of four muscles that wrap around the ball of your shoulder joint, holding it snugly in its shallow socket. These muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis, often remembered by the acronym SITS. Each one connects your shoulder blade (scapula) to your upper arm bone (humerus), and together they make it possible to lift, rotate, and reach with your arm while keeping the joint stable.
How the Four Muscles Work Together
Your shoulder socket is remarkably shallow, more like a golf ball sitting on a tee than a ball locked into a deep cup. That design gives you an enormous range of motion, but it also means the joint relies heavily on muscles rather than bone structure for stability. The rotator cuff muscles surround the joint capsule and create balanced opposing forces that keep the head of the humerus centered in the socket during movement.
When you lift your arm out to the side, the rotator cuff presses the ball of the joint downward into the socket so your larger deltoid muscle can raise the arm without jamming bone against bone. The subscapularis pulls from the front while the infraspinatus and teres minor pull from the back, preventing the humerus from sliding forward or backward. The supraspinatus resists the constant downward pull of gravity on the weight of your arm. This coordinated system of opposing forces is what orthopedic specialists call “dynamic stabilization,” and it’s active during virtually every shoulder movement you make.
The Supraspinatus
The supraspinatus sits on top of the shoulder blade and runs to the highest point of the humeral head. Its primary job is initiating the motion of lifting your arm away from your body. It’s also the most commonly injured rotator cuff muscle, partly because its tendon passes through a narrow space beneath the bony tip of the shoulder blade (the acromion). That tight corridor makes it vulnerable to compression and wear over time.
Doctors test the supraspinatus with what’s called the Jobe test (sometimes called the “empty can” test), where you hold your arms out in front of you at an angle with your thumbs pointing down, then resist downward pressure. This test picks up about 88% of supraspinatus tears, making it one of the more reliable clinical exams for rotator cuff injury.
The Infraspinatus and Teres Minor
These two muscles form the back wall of the rotator cuff. The infraspinatus covers the lower portion of the shoulder blade and attaches to the humerus just behind the supraspinatus. The teres minor sits beneath it, running from the outer edge of the shoulder blade to the humerus. Both muscles externally rotate your arm, the motion you use when pulling your hand away from your stomach or cocking your arm back to throw.
Together, they also compress the joint and resist the humerus from sliding forward or upward in the socket. Weakness in these posterior muscles is common in overhead athletes like swimmers, volleyball players, and baseball pitchers, where repetitive internal rotation gradually overpowers the external rotators. Clinical tests for infraspinatus tears tend to be highly specific (meaning a positive result is reliable) but not very sensitive, so a negative test doesn’t necessarily rule out a problem.
The Subscapularis
The subscapularis is the only rotator cuff muscle on the front side of the shoulder blade. It’s actually the largest and strongest of the four, and it sits sandwiched between the scapula and the rib cage. It stretches from the inner surface of the shoulder blade to the lower part of the humeral head, and its main action is internal rotation, the motion of reaching behind your back or rotating your arm inward.
It also serves as the primary anterior stabilizer, preventing the ball of the joint from slipping forward out of the socket. Doctors test the subscapularis with maneuvers like the belly-press or bear hug test, where you press your hand against your abdomen or grab the opposite shoulder and resist being pulled away. Like infraspinatus tests, these exams tend to catch tears when they’re positive but can miss smaller injuries.
What Goes Wrong: Tears and Tendinopathy
Rotator cuff problems are extremely common, affecting between 7% and 22% of people over age 40. The prevalence climbs steadily with age: up to 50% of people over 80 have some degree of rotator cuff tearing. Here’s the surprising part. The vast majority of those tears never cause symptoms. In studies of people with no shoulder pain (average age around 44), full-thickness tears showed up on MRI in about 10% of cases. Fewer than 5% of all rotator cuff tears ever require surgery.
Three overlapping conditions account for most rotator cuff pain:
- Tendinopathy (tendinosis): Degeneration of the tendon tissue from repetitive overuse. This is a breakdown in the tendon’s structure rather than active inflammation, though the terms “tendonitis” and “tendinopathy” are often used interchangeably.
- Subacromial bursitis: Inflammation of the fluid-filled sac that cushions the space between the acromion and the supraspinatus tendon. It often develops alongside tendinopathy.
- Rotator cuff tears: Partial or full-thickness breaks in the tendon, which can result from gradual degeneration or a sudden injury like a fall. Untreated tendinopathy can progress to tearing over time.
These conditions frequently overlap. Someone with longstanding tendinopathy may develop bursitis from the altered mechanics, and a degenerating tendon is more susceptible to tearing. An X-ray can rule out arthritis or calcium deposits but can’t show the rotator cuff itself. Ultrasound or MRI is needed to visualize tears directly.
Treatment: Physical Therapy First
For partial-thickness tears (those that don’t go all the way through the tendon), physical therapy is the first-line treatment. The 2025 guidelines from the American Academy of Orthopaedic Surgeons recommend rehab for low-grade and intermediate-grade partial tears, with surgery reserved for people who still have significant pain and functional limitations after a genuine course of therapy. For high-grade partial tears that don’t respond to conservative treatment, surgical repair has strong evidence supporting improved outcomes.
The goal of rehab is to strengthen the remaining rotator cuff muscles so they can compensate for the damaged tissue, restore balanced force couples around the joint, and gradually rebuild shoulder function. This typically involves progressive resistance exercises targeting external rotation, scapular stability, and controlled overhead strengthening. Many people with partial tears and even some with full-thickness tears regain functional, pain-free shoulders without surgery.
For massive tears that can’t be repaired, particularly when the joint itself has developed arthritis, a specialized joint replacement (reverse shoulder arthroplasty) may be considered after other treatments have failed. This is a last-resort option supported by limited but positive evidence.
Keeping the Rotator Cuff Healthy
Because the rotator cuff muscles are small relative to the larger muscles that power shoulder movement (the deltoid, pectorals, and lats), they’re easy to neglect in a typical workout routine. Strengthening external rotation with a resistance band, performing prone shoulder exercises that target the posterior cuff, and maintaining good scapular control all help protect the rotator cuff from the repetitive strain that leads to tendinopathy. People who do repetitive overhead work, whether throwing a ball, painting ceilings, or stocking shelves, benefit most from deliberate rotator cuff training because the demand on those small stabilizers is highest when the arm is elevated and rotating.