Shoulder impingement is pain from a rotator cuff tendon, and the small fluid-filled sac that cushions it, being squeezed or irritated at the top of the shoulder as the arm rises. What people tend to notice is a band of pain partway through lifting the arm out to the side, easing again once the arm is higher.
The gap for the tendon is tightest mid-lift and opens again higher up
That gap sits under the acromion, the bony shelf at the outer end of the shoulder blade, which is why some clinicians call this subacromial pain. With the arm by your side there is room to spare. As the arm rises, the top of the upper arm bone, where the tendon attaches, turns up towards the shelf, and the squeeze is usually felt between roughly 60 and 120 degrees, from a little below shoulder height to a little above it. Past that, the arm bone rotates outward and the shoulder blade turns upward against the ribs, so the tendon slips under the edge of the shelf instead of pressing into it.
The name for this is a painful arc. It is a pattern, not a diagnosis, and a torn tendon or a problem in the neck can hurt in much the same place.
Frozen shoulder is stiff in every direction, impingement hurts in one band
Both make reaching up miserable, and the difference is in what the shoulder can still do. With impingement the arm usually still gets to the top, with a wince on the way, and if someone lifts it for you while your muscles stay relaxed it often goes higher and hurts less. In a frozen shoulder the joint capsule itself has thickened and tightened, so the arm stops at the same point however it is moved, and turning the forearm outward with the elbow tucked in is often the hardest movement of all.
A rounded upper back tips the shoulder blade forward and narrows the gap
The shoulder blade, which the arm lifts from, rests on the upper ribs. When the upper back rounds through a long laptop day, the blade tips forward and drifts round the ribcage, so the shelf over the tendon starts lower and rises less as the arm goes up.
You can feel this for yourself. Slump, lift one arm slowly out to the side and notice where it catches, then sit tall with your head back over your shoulders and try again. For plenty of people the arm gets higher before it complains. Posture is rarely the only reason a shoulder hurts, but it is the part that changes hour by hour. Forward head posture often comes with a rounded upper back, and how posture is measured is set out under posture correction.
Overhead reaching and lying on the sore side keep the tendon irritated
Hanging washing on a high line takes the tendon through the tight band, and so does a week of swimming laps after months at a desk. Nights count as well. Lying on the sore side with that arm tucked under the pillow presses on the same spot for hours, and on a hot, humid night it is easy to wake with the arm flung overhead. Resting the arm completely tends to leave it stiffer, so the usual advice is to spread overhead jobs out rather than stop moving, unless a doctor has said otherwise.
The Sync measures and supports movement, and leaves medical decisions to doctors
A visit starts with assessment and measurement: how the upper back and neck are moving, with the readings on the screen as they are taken, and where in the lift the pain begins. Computer-guided spinal mobilisation through SpinalSync and soft tissue work around the shoulder through MyoSync are there to support comfort and movement. Later visits re-measure against that first reading, so any change is visible rather than taken on trust. Whether a rotator cuff tendon is torn, and whether an injection or surgery is worth discussing, is for a doctor to decide. The Sync does not diagnose, prescribe medication, inject, operate, or provide or read imaging, and a Sync specialist says early when a doctor is the better next step.
Common questions about impingement
No, though the two can occur together. Impingement describes a tendon being irritated as the arm lifts, while a tear is damage to the tendon itself. Weakness that came on suddenly after a fall or a heavy lift is a reason to see a doctor, who decides whether imaging is needed.
It is often felt on the outside of the upper arm rather than on top of the shoulder, which surprises people. Pain that travels below the elbow, especially with numbness or tingling, more often comes from the neck and is worth raising with a doctor.
Lying on your back, or on the other side with the sore arm resting on a pillow in front of you, keeps weight off the shoulder and the arm out of the overhead position. A pillow tucked behind your back makes it harder to roll onto the sore side during the night.
Not always. That decision belongs to a doctor, who usually examines the shoulder first and arranges an ultrasound or MRI if something such as a tear is suspected. The Sync does not provide or read imaging.
Written by the Aphyx Content team, reviewed by the clinical team at The Sync. Published 2 October 2026. Last updated 2 October 2026.