Infraspinatus Muscle: Action, Insertion & Origin

Instructor: Dan Washmuth

Dan has taught college Nutrition, Anatomy, Physiology, and Sports Nutrition courses and has a master's degree in Dietetics & Nutrition.

The infraspinatus is an important muscle of the shoulder, which is one of the most mobile joints in the human body. Become knowledgeable of infraspinatus by checking out this lesson on the origin, insertion, and action of this muscle.

Muscle of the Rotator Cuff

Try this at home:

  1. Raise your arms at to your sides and then lower them back down
  2. Raise your arms to your front and then lower them back down
  3. Now perform two arm circles in the forward direction
  4. Now perform two arms circles in the backward direction

This incredible range of motion is due to our infraspinatus muscle, a triangular-shaped muscle located at the back of the shoulder. It is one of the four muscles that make up the rotator cuff of the shoulder joint. One of the main functions of the rotator cuff is to maintain shoulder stability while the arm moves around the shoulder.

Origin of the Infraspinatus

The infraspinatus muscle originates from the scapula, otherwise known as the shoulder blade. More specifically, this muscle originates from the infraspinous fossa of the scapula. The infraspinous fossa is the large, triangular-shaped concave surface at the back of the scapula. The infraspinous fossa contributes to both the shape and name of the infraspinatus muscle.

The infraspinatus muscle originates from the infraspinous fossa at the back side of the scapula.
infraspinous fossa

Insertion of the Infraspinatus

From the infraspinous fossa, the infraspinatus muscle travels upward diagonally and inserts onto the top of the humerus, which is the long bone of the upper arm. Specifically, the infraspinatus inserts onto a large, round prominence located at the top, outer portion of the humerus. This prominence is called the greater tubercle or greater tuberosity.

The infraspinatus muscle inserts onto the greater tubercle of the humerus.
greater tubercle

What Does the Infraspinatus Do?

The infraspinatus muscle is responsible for a couple different actions. The following chart describes these actions.

Action of Infraspinatus Description of Action
Stabilization of shoulder joint The infraspinatus helps to maintain shoulder stability by keeping the head of the humerus in its proper position against the scapula while the upper arm moves throughout the shoulder joint.
Lateral rotation of the humerus The infraspinatus causes lateral (external) rotation of the humerus. This action involves the outward turning or twisting of the arm, such as when a person rotates their arm outward as they pull a door open.

One of the actions of the infraspinatus muscle is to keep the head of the humerus in its correct location against the scapula.
shoulder joint

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