The infraspinatus: why the back of your shoulder blade makes the front of your shoulder hurt

The infraspinatus fills the broad hollow on the back of the shoulder blade, below the bony ridge you can feel (the spine of the scapula). Its job is to rotate the arm outward and to hold the head of the humerus centred in the socket while stronger muscles move the arm. It is one of the hardest-working muscles of the rotator cuff, and its trigger points are among the most common in the entire body (travell1942, simons2004).

What makes it clinically famous is where the pain goes. Infraspinatus trigger points refer deep into the front of the shoulder — patients describe it as pain 'inside the joint' — and often down the outside of the arm, sometimes reaching the forearm and the thumb side of the hand. Because the pain is felt where nothing is wrong, it is routinely attributed to the biceps tendon, the joint itself, or 'impingement', while the actual source sits untouched on the back of the scapula. Travell considered it the single most overlooked cause of front-of-shoulder pain (travell1942).

For the terminology and interpretation used here, compare What are trigger points?; Primary vs secondary trigger points; How to read referred pain maps. These guides distinguish the definition of a trigger point, its classification and the limits of a referred-pain map.

Two very different groups share this muscle. The first is anyone who loads the shoulder repeatedly overhead or at speed: throwers, swimmers, tennis and volleyball players, climbers, weightlifters. The infraspinatus works as a brake in the follow-through of a throw, and eccentric braking is exactly the kind of load that produces trigger points (simons2004, bron2011).

The second group never throws anything: desk workers. Hours with the arms held forward on a keyboard keep the infraspinatus in a long, low-grade contraction to stabilise the shoulder blade, and sustained low-level load is the other classic route to trigger point formation (ge2011, gerwin2004). Sleeping on the painful side with the arm trapped under the body is a common aggravator, and many people first notice the problem as night pain that wakes them when they roll onto that shoulder.

A frequent trigger is a single unaccustomed effort — a weekend of painting a ceiling, a long drive with the arm up on the wheel, a first climbing session — after which the front-of-shoulder ache appears a day or two later and is blamed on the joint.

You cannot easily press your own infraspinatus with your fingers, so use a ball. Stand with your back to a wall, place a tennis or lacrosse ball over the back of the shoulder blade on the painful side — in the broad area just below the bony ridge, roughly halfway between the spine and the outer edge of the blade — and lean your weight into it. Explore slowly.

The finding that matters is not generic soreness: it is a specific spot whose pressure reproduces your familiar front-of-shoulder pain, or sends a distinct ache down the arm. That reproduction of the recognisable complaint is the single most useful sign that the muscle is the source (simons2004, lucas2009). Most people are surprised by how tender these points are — infraspinatus trigger points are often exquisitely sore even in people with no shoulder complaint at all, which is why the reproduction of your pain, not the tenderness alone, is the criterion.

A useful confirmation: reach behind your back as if to tuck in a shirt. If that movement is limited and pulls painfully at the front of the shoulder, and pressing the spot on the scapula eases it within a minute or two, the infraspinatus is almost certainly involved.

Self-treatment works well for this muscle because it is superficial and easy to load with a ball. Hold sustained pressure on the reproducing spot — enough to feel a strong but tolerable ache — for 30 to 90 seconds, until the ache eases, then take the arm slowly through its range: across the chest, then behind the back. Repeat once or twice a day. Evidence for sustained pressure and for needling of shoulder-girdle trigger points is consistent in reducing pain, though both work better combined with movement and load management than alone (cummings2001, moraska2017, vier2019).

Two cautions. First, do not stretch aggressively into the painful front of the shoulder in the early days: the classic 'sleeper stretch' helps some people and provokes others; keep every stretch slow and mild. Second, treat the neighbourhood. The infraspinatus rarely works alone — the teres minor beside it, the supraspinatus above the ridge, and the upper trapezius and levator scapulae above the shoulder commonly share the load and the trigger points, and a plan that treats only one muscle is the usual reason a good plan underperforms (travell1942, simons2004).

Expect change on the timescale of weeks, not days: a typical course is two to four weeks of daily self-treatment, with the night pain usually improving first. If four to six weeks of consistent work produce no change, or the shoulder is genuinely weak — you cannot hold the arm out against light resistance, or it gives way — that is no longer a self-care problem and deserves an examination (quintner2015).