• The trapezius muscle adducts and upwardly (laterally) rotates the scapula.
• The upper fibers are more suited for movement, and elevate the scapula.
• The middle and lower fibers maintain the vertical and horizontal position of the scapula rather than generate torque.  They are better suited for stabilization, working at a constant length to resist protraction of the scapula by the serratus anterior.
• Some authors suggest that the middle fibers adduct the scapula, while the lower fibers depress the scapula.  Thus, when the upper trap is short and the lower fibers are overstretched and weak the entire shoulder girdle will be elevated, rather than upwardly rotated.
• When he upper trapezius is short, and the shoulder girdle is posturally elevated, the entire shoulder, including the distal end of the acromiom, should be elevated.
• If the upper trap is overstretched and weak and the lower fibers are short and facilitated, the shoulder may be depressed.
• If the scapula fails to elevate during shoulder flexion or abduction, the action of the upper trapezius is considered to be insufficient.
• If the middle fibers are short and tight, adduction may dominate over abduction.

ACTIONS:

UPPER FIBERS

BILATERALLY

• Extend the head and neck

UNILATERALLY

• Laterally flex the head and neck to the same side
• Rotate the head and neck to the opposite side
• Elevate the scapula
• Upwardly rotate the scapula

MIDDLE FIBERS

• Adduct the scapula
• Stabilize the scapula

LOWER FIBERS

• Depress the scapula
• Upwardly rotate the scapula

ORIGIN:

• External occipital protuberance, medial portion of the superior nuchal line of the occiput, ligamentum nuchae, and the spinous process of c-7 through t-12

INSERTION:

• Lateral 1/3 of the clavicle, acromiom, and spine of the scapula

NERVE INNERVATION:

• Spinal accessory and cervical plexus