Infraspinatus Muscle: Location and Actions

The infraspinatus muscle is a thick, triangular muscle which occupies most of the concave, dorsal surface of the scapula, a part of the scapula called the infraspinatus fossa. In other words, this muscle covers almost the entire scapula (shoulder blade) below the scapular spine.

See infraspinatus Trigger Points

The muscle gets its name from its location: Spinatus refers to the spine of the scapula and infra means below or beneath. Use the labeled image of the scapula below to locate its different parts.

infraspinatus muscle illustration labeled

Together with the subscapularis, supraspinatus, and teres minor, the infraspinatus helps make up the rotator cuff. This group of muscles, which contribute to external and internal rotation of the shoulder, have angles of pull that allow them to provide dynamic stabilization of the shoulder joint, assisting to stabilize the humeral head in the glenoid fossa. The rotator cuff, along with the deltoid muscle, makes up one of the most important force couples in the body. The muscle is innervated by the suprascapular nerve.

What is a force couple? A force couple is a pair of muscle that produces forces that act together on a joint to produce rotation. These forces may actually exert pulls in opposite directions. These muscles may be synergistic pairs, consisting of prime movers and groups of stabilizers, for instance, or agonist/antagonist pairs. Force couple, then, is actually another way of referring to muscle synergists or a synergistic action.

Kinesiology: The Skeletal System and Muscle Function

Infraspinatus Origin, Insertion, and Action

Origin: The infraspinatus, in most cases, has three pennate origins on the infraspinatus fossa just below the spine of the scapula.

Insertion: Posterior of greater tubercle of the humerus.

Action: External rotation of the glenohumeral joint, together with teres minor; horizontal abduction of the glenohumeral joint, extension of the glenohumeral joint, stabilization of the humeral head in the glenoid fossa. 1Simons, David G., Janet G. Travell, Lois S. Simons, and Janet G. Travell. “Chp. 8: Masseter Muscle.” Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual. Baltimore: Williams & Wilkins, 1999. 329. Print.,2Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998.

See Infraspinatus Trigger Points and Referred Pain

Sources   [ + ]

1. Simons, David G., Janet G. Travell, Lois S. Simons, and Janet G. Travell. “Chp. 8: Masseter Muscle.” Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual. Baltimore: Williams & Wilkins, 1999. 329. Print.
2. Floyd, R. T., and Clem W. Thompson. Manual of Structural Kinesiology. Dubuque, IA: WCB/McGraw-Hill, 1998.