Teres minor

The teres minor starts at the outer border of the shoulder blade (Scapula) and attaches to the lower facet of the greater tubercle of the upper arm bone (Humerus). The “round” in its Korean name refers to its slender, rounded shape. It runs alongside the Infraspinatus muscle just above it, and the two often work together almost as a single unit. It is supplied by the axillary nerve, which passes through the armpit region.

The teres minor forms the Rotator cuff together with the Supraspinatus muscle, infraspinatus, and Subscapularis. In the shoulder joint, the head of the humerus rests in a shallow socket, allowing a wide range of movement but also making it prone to instability. The four rotator cuff muscles hold the humeral head from all sides, keeping the joint in place as you move your arm.

The teres minor has two jobs.

• Rotating the arm outward (external rotation) — It works with the infraspinatus when you rotate your arm outward so that your palm faces up. It also helps a little with bringing the arm toward the body.
• Holding the humeral head in place — When you raise your arm, it presses the humeral head downward and backward to keep it from being pushed upward toward the Acromion. Small as it is, it helps the shoulder move smoothly.

The teres minor is involved in more movements than you might think.

• When you rotate your arms back to wash or tie up your hair
• When you pull your arm out of a sleeve or reach behind you to pick something up
• When it gently slows the arm as it swings forward after a tennis serve or baseball pitch
• When you bring your arm out of the water and swing it forward while swimming

If you play a sport that repeats these movements, the back of your shoulder may feel sore or heavy. Often, the muscles at the back of the shoulder are fatigued together rather than just one muscle hurting. The Fascia surrounding the muscles connects with the neighboring infraspinatus and the posterior fibers of the deltoid, so stiffness in one area is understood to affect the surrounding areas as well.

• Gentle external rotation exercises — Keep your elbow against your side and bend it to 90 degrees. Hold a resistance band, slowly rotate your hand outward, then return. Doing 10–15 repetitions at a time with a light band can strengthen the teres minor and infraspinatus together. Placing a towel under your armpit makes it easier to keep your elbow close to your body.
• Stretching the back of the shoulder — Extend one arm across the front of your chest, then use your other hand to pull near the elbow toward your body and hold the stretch for 20–30 seconds. A pulling sensation at the back of the shoulder is enough.
• Loosening up with shoulder shrugs — Raise your shoulders toward your ears, roll them back, and let them drop to loosen the area around your shoulder blades.
• Changing your smartphone and keyboard posture — Staying with your shoulders rounded forward for a long time keeps the muscles at the back stretched, which can tire them out. Try opening your shoulders back once an hour.

Start exercising gently when your shoulder is warm. If you feel sharp, shooting pain, stop and try a smaller angle. Working on Shoulder mobility as well can make movement more comfortable.

If you have stabbing pain at the front or side of your shoulder when raising your arm, shoulder pain that wakes you when lying down at night, or a noticeable loss of strength in your arm, it is worth having the overall condition of your shoulder checked. Rather than viewing it as a problem with just one muscle, it is more appropriate to look at coordination across the whole shoulder, as with Shoulder impingement syndrome. If you also have numbness or tingling in your hand, have possible neck or nerve problems checked as well.