Back of Shoulder Muscles: What Each One Does

The back of shoulder muscles are a group of layers that reach your arm behind you, turn it outward, and keep the ball of the upper arm centred in its socket. Some sit on the shoulder blade itself. Others sit on the ribs and spine and move the shoulder blade around. I teach the Feldenkrais Method®, so I like anatomy that helps you feel your own shoulder. This tour keeps the names simple and asks what each muscle does in daily life.

A quick map of the muscles in the back of the shoulder

Picture the shoulder from behind. The round cap of muscle on the outside is the deltoid, and its rear third is the posterior deltoid. Under it sits the shoulder blade, a flat triangle of bone that rests on the back of your ribs. Several small muscles cover that bone, and larger ones run from it to your spine.

Your shoulder joint is a ball and socket, but the socket is shallow. The muscles around it do a lot of the holding, so they are busy even when you are only sitting.

The posterior deltoid: reaching behind you

The posterior deltoid is the rear part of the shoulder cap. It starts on the spine of the shoulder blade and ends on the upper arm bone. When you reach back for a seat belt or pull your arm behind you to put on a coat, this muscle works. It also helps swing the arm out to the side and turn it outward.

The rotator cuff on the back of the shoulder blade

The rotator cuff is a group of four small muscles that wrap the ball of the joint. Three of them lie on the back of the shoulder blade or its top edge.

• Infraspinatus. This is a broad, flat muscle on the back of the shoulder blade, below its bony ridge. It turns the arm outward, as when you open a door wide or reach out to greet someone.
• Teres minor. A thin muscle just below the infraspinatus. It helps turn the arm outward and keeps the ball snug in the socket.
• Supraspinatus. This one sits on top, above the bony ridge. It helps lift the arm to the side, and it also steadies the joint.

The fourth cuff muscle sits at the front of the shoulder blade. Together, the four make tiny adjustments all day. You rarely feel them working until they tire.

Teres major and the latissimus dorsi

The teres major runs from the lower edge of the shoulder blade to the upper arm. People sometimes call it the little helper of the lats. It brings the arm down and back, and turns it inward. You use it when you pull a drawer toward you.

The latissimus dorsi, or lats, is the widest muscle of the back. It starts low, from the spine and pelvis, and sweeps up to the upper arm near the armpit. It pulls the arm down toward your body and behind you. Because it links your arm with your pelvis, a reach with one arm can be felt down the side of the back.

The shoulder blade movers seen from behind

The shoulder blade is held to the ribcage by muscles, not by a joint. That gives it great freedom. It can glide up, down, toward the spine and away, and it can tilt as you reach overhead.

• Rhomboids. These lie between your spine and the inner edge of the shoulder blade. Their pull brings the blade closer to the midline and keeps it snug on the ribs.
• Middle trapezius. Its fibres run sideways and draw the blades back, as when you pull a heavy door toward you.
• Lower trapezius. These fibres draw the shoulder blade down and help it turn upward when you reach to a high shelf.
• Levator scapulae. It runs from the neck to the top inner corner of the blade and lifts it, for example when you hunch against the cold.

When these muscles and the cuff share the job well, a reach feels smooth. When one group does most of it, that group aches. Our Feldypedia article on neck and shoulder tension looks at how this can build up.

Why the back of the shoulder feels sore after reaching all day

Typing, driving, cooking and holding a phone all keep your arms in front of you. The front of the shoulder stays short, and the back of shoulder muscles hold the arm against the pull of gravity. A muscle that holds a small effort for hours tires faster than one that moves and rests.

A few patterns come up again and again in my classes.

• Arms in front for hours. The rear muscles work as brakes without ever getting a break.
• A still ribcage. When the ribs and the spine between the shoulder blades barely move, the shoulder blade has less room to glide. The cuff then works harder for each reach.
• Shallow breathing. Small breaths mean the ribs hardly move, so the shoulder blade has a quieter surface to rest on.
• Carrying and gripping. A heavy bag or a tight grip invites the shoulder to hold up the whole arm.

Worldwide, about 1.71 billion people live with a musculoskeletal condition (WHO, 2022). Aching shoulders are part of that large picture. If this sounds familiar, the explainer on why your shoulders feel so tight goes further.

Where a frozen shoulder fits in

A frozen shoulder, called adhesive capsulitis, is mainly a problem of the joint capsule. The capsule is the soft sleeve around the ball and socket. It is not a muscle problem, although nearby muscles often tighten in response. Early on, turning the arm outward is usually the first movement to feel limited. That is one reason people with a frozen shoulder get curious about the infraspinatus and teres minor. A clinician can tell you what is happening in your own shoulder.

A small experiment: how the shoulder blade glides

Sit toward the front of a chair. Rest your right hand on your left shoulder blade, as far as you can reach. Slowly lift your left arm forward a little, and then lower it. Notice what your hand feels. Does the shoulder blade slide, tip or stay still?

Now let your ribs and head turn a little to the left as the arm moves. Do it again, slowly. Does the blade glide more freely when the ribs join in? Nothing needs to be achieved. You are only sensing how each part takes its share.

How a Feldenkrais® approach works with the back of the shoulder

Advice about shoulder muscles often picks one muscle and stretches or strengthens it. That has its place. The Feldenkrais Method asks a different question: how are the shoulder blade, ribs and spine organised together? When the ribs and spine move a little at each level, the shoulder blade often finds more freedom. The muscles around it may then hold less.

In an Awareness Through Movement® lesson you move slowly, often lying down. You sense which areas move along and which stay quiet. You might lift one arm while sensing the ribs on that side. Many people find that a shoulder begins to move more easily, even when the lesson barely touched the shoulder. Feldy offers short audio lessons like this, which you follow at home. The frozen shoulder page shows how they are shaped for this area. For gentle movement ideas, see our guide to frozen shoulder stretches.

Alongside clinical care and other methods

Your doctor or physiotherapist can work in parallel with you, and this practice never replaces that care. Physiotherapy can assess your shoulder and guide your rehabilitation. Other methods, such as yoga, Pilates, stretching and strength work, are different options with their own mechanisms. To ease the tight, hunched feeling of a long day, the guide on how to loosen tight shoulders is a good next step.

Common Questions about back of shoulder muscles (FAQ)

Is it safe to move when the back of my shoulder is sore?

For ordinary muscle soreness, small and slow movement is usually fine. Keep it well inside comfort and stop if the pain turns sharp. Be more careful after a fall or injury, or if the arm feels weak or numb. In those cases, have it checked before you move it at home.

How often should I move my shoulder muscles gently?

A few minutes on most days works better than one long session. Short pauses during a desk day count too. The movements stay small and easy, so your muscles do not need rest days between them.

How long until the back of my shoulder feels different?

Some people notice a little more ease within one session. A steadier change usually takes a few weeks of regular practice. Old habits can take more time. If nothing shifts after several weeks, speak with a clinician.

How is this different from rotator cuff band exercises?

Band exercises train single muscles against resistance, and many people find them useful. A Feldenkrais approach uses slow, light movement to notice how the shoulder blade, ribs and spine share the work. The two use different mechanisms, and some people enjoy both.

What is the best way to ease an aching back of the shoulder?

For many people, the best way is gentle movement that includes the ribs and shoulder blade, not just the sore spot. Changing position often, resting the arms on a support, and easy breathing help too. Heat or massage can feel pleasant alongside this.

Which signs mean I should see a professional about my shoulder?

Get it checked if pain began after a fall, if the arm turns weak all of a sudden, or will not lift. Night pain, or pain that keeps growing, deserves a visit too. Pain with chest tightness or breathlessness needs emergency care: call emergency services straight away.

Is a frozen shoulder a muscle problem?

A frozen shoulder, or adhesive capsulitis, mainly involves the joint capsule, the soft tissue wrapped around the joint. Muscles often tighten around it, though. Turning the arm outward is usually the first movement to feel limited. A clinician can tell you what is going on in your shoulder.