Shoulder Pain: Rotator Cuff Injury, Impingement, or a Muscle That Isn't Working?

Shoulder pain can be frustrating because several very different problems can feel almost identical at first. It hurts to lift the arm. It hurts to reach behind you. Maybe you cannot sleep on that side. Maybe somebody has already told you that you have "impingement" or a rotator cuff problem.

Those are real possibilities. The question is whether the painful tissue is injured, irritated because of the way the shoulder is moving, or both.

The Shoulder Needs Motion and Stability at the Same Time

The shoulder gets its tremendous range of motion by sacrificing some of the bony stability that you have at a joint like the hip. The humeral head, shoulder blade, collarbone, rotator cuff, and surrounding muscles all have to coordinate as the arm moves.

The rotator cuff includes the supraspinatus, infraspinatus, teres minor, and subscapularis. Those muscles do much more than rotate the arm. Together they help keep the humeral head controlled in the socket while larger muscles like the deltoid generate movement.

What "Impingement" Actually Describes

With shoulder impingement, the tissues beneath the acromion can become irritated as the arm is elevated. The bursa and rotator cuff tendons are common pain generators. But saying something is being impinged still leaves another question: why is the space being loaded that way?

Sometimes there is a structural reason, such as a significant tendon tear or bony change. Sometimes inflammation follows repetitive overhead activity. And sometimes the mechanics of the scapula and humeral head are simply not being controlled well.

Scapular Rhythm Matters

Every time you lift your arm, the shoulder blade should rotate and move with the arm. The serratus anterior and different divisions of the trapezius are major players in that motion. If the scapula does not upwardly rotate or stabilize appropriately, the rotator cuff may have to work in a mechanically disadvantaged position.

The pectoral muscles, latissimus, rhomboids, and even the position of the rib cage can change that movement. This is why I rarely look at a painful shoulder as just a ball-and-socket joint. The shoulder blade and thorax are part of the same system.

A Weak Test Does Not Automatically Mean a Torn Muscle

This is an important distinction in Applied Kinesiology. A muscle that does not respond normally to a manual muscle test is not automatically torn. The test may indicate altered recruitment, pain inhibition, neurologic influence, or another functional problem. A structural tear has to be identified with the appropriate orthopedic examination and, when necessary, ultrasound or MRI.

That difference changes treatment. If the supraspinatus tendon is significantly torn, the plan is not simply to "activate the supraspinatus." If the tendon is intact but the muscle is inhibited while the deltoid, upper trapezius, and other muscles are compensating, then restoring the balance of the movement pattern may be much more relevant.

Two People, Same Shoulder Pain, Different Pattern

One person may have pain lifting the arm because the supraspinatus tendon is irritated after repetitive overhead work. Another may have good rotator cuff tissue but poor serratus and lower-trapezius control, changing the position of the scapula. A third may have a cervical nerve problem that produces weakness and shoulder pain even though the shoulder joint itself is not the primary issue.

The symptom "shoulder pain" is the starting point. It is not the conclusion.

When Imaging or Further Evaluation Matters

A sudden injury followed by major weakness, inability to lift the arm, deformity, repeated dislocation, significant swelling, or persistent night pain deserves a careful structural evaluation. Progressive numbness or weakness into the arm can also point toward cervical or peripheral nerve involvement.

The goal is not to avoid imaging when it is appropriate. The goal is to use it for the question it actually answers: is there structural damage, and does that damage fit the clinical pattern?

The Takeaway

Shoulder pain may come from a rotator cuff tendon, bursa, joint, nerve, or an altered movement pattern involving several muscles at once. Treating the painful spot without restoring the mechanics that load it is one reason shoulder pain can keep returning.

Before deciding what the shoulder needs, find out what the shoulder is actually doing.

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Sources

American Academy of Orthopaedic Surgeons (AAOS), OrthoInfo. Shoulder Impingement/Rotator Cuff Tendinitis.

American Academy of Orthopaedic Surgeons (AAOS), OrthoInfo. Rotator Cuff Tears. Updated March 25, 2026.

Walther DS. Applied Kinesiology Synopsis. 2nd ed. Systems DC; 2000. See Shoulder and Shoulder Girdle and rotator-cuff muscle testing sections.