Teres Minor Muscle: Action, Origin & Insertion

Instructor: Joshua Bowles

Joshua is a Sports Medicine and Athletic Training Instructor and has a Master's degree in Kinesiology.

In this lesson we will discuss the teres minor muscle, where it's located, and the specific actions it allows. We will also cover a brief anatomical overview including the origin and insertion points.

The Amazing Shoulder

The shoulder allows for more movements than any other joint in the body. Because of this, we are able to do amazing things with it, most of which we take for granted. That is, until we lose function or have pain associated with it.

There are many muscles that help make these movements possible. One key muscle that we will look at in this lesson is the teres minor.

Teres Minor Shape

All muscles are named based on various features including size, shape, action and even location. The same is true for the teres minor muscle. 'Teres' means 'round in shape', while 'minor' means 'small'.

The muscle itself is rounded in shape. It's not circular, but rather more like a cylinder, if you want to think of it in three dimensional terms. In anatomy, if there is a muscle named for being large then there is typically another muscle named for being small to differentiate them. So, as you might expect, there is also a teres major, which sits directly below the teres minor.

The shoulder joint; the teres minor muscle is highlighted in red
Teres minor of the shoulder

Action

The teres minor is a part of a group of shoulder muscles called the rotator cuff. The other three muscles in this group include the supraspinatus, infraspinatus, and the subscapularis, and all have a role in the movement of the shoulder.

The main function of the teres minor is a movement called external rotation, primarily at 90 degrees. This is the movement of the upper arm bone, known as the humerus, rotating away from the center of the body. The infraspinatus muscle assists the teres minor in this movement.

Imagine placing your left elbow up to about shoulder level with your arm bent making an 'L'. External rotation at 90 degrees, sometimes referred to as 'horizontal external rotation', is the movement of taking your hand and moving it straight back while keeping your elbow in that fixed position.

The teres minor also aids in the movements of shoulder extension, which is moving your arm straight backward from a neutral position by your side; and adduction, which is the movement of your humerus towards your body.

Have you ever thrown a ball, performed jumping jacks, or painted a wall? Or perhaps you've braced yourself from falling backwards? If so, then you have used the teres minor in some capacity. This muscle is used all the time in our daily lives to perform various small functions in our shoulder.

Origin and Insertion

The origin of a muscle is where it begins. The teres minor originates on the lateral border of the scapula, in other words, the outer edge of the shoulder blade that is closest to the spine.

The teres minor muscle originates on the lateral border of the scapula (highlighted)
lateral border on scapula

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