Infraspinatus

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Other Names

  • Rotatory Cuff
  • Back

Heads

  • Superior
  • Middle
  • Inferior

Movement

Shoulder

Attachments

Origin

  • Scapula (Medial)
    • Infraspinous fossa

Insertion

  • Humerus
    • Greater Tubercle (Posterior)
      • Middle Facet

Related Muscles

The infraspinatus is the second most often injured rotator cuff muscle. It is assisted by the Teres Minor. See other rotator cuff muscles:

Infraspinatus

Comments

Infraspinatus is somewhat more effective external rotator at lower shoulder abduction angles. All heads of the infraspinatus have their largest ER moment arm (approximately 2.2 cm) and generate their greatest torque at 0° shoulder abduction. As shoulder abduction angle increases, moment arms of inferior and middle heads stay relatively constant, while moment arm of superior head progressively decreases until it is about 1.3 cm at 60° abduction. (Otis JC, et al. 1994)

Exercises in 90° abducted position are typically incorporated to simulate position and strain on shoulder during overhead activities such as throwing.

Infraspinatus exerts an average of 5.71 and 6.5 times more shoulder external rotation force than does Teres Minor in both 0° and 90° abducted shoulder positions, respectively (Hughes RE & An KN 1996).

Infraspinatus appears to be involved in abduction on scapular plane (Hughes RE & An KN, 1996; Otis JC, et al. 1994) with very small moment arm at 0° and approximately 1 cm abductor moment arm beyond 15° shoulder abduction (Liu J et al. 1997).

See infraspinatus weakness.

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