The trapezius muscle, located beneath the skin of the neck and back, forms a triangular shape on each side, coming together to create a trapezoid across the back. It connects the scapular bones to the skull base and vertebrae, playing a crucial role in suspending the shoulder girdle.

Functional Anatomy

The trapezius originates from the external occipital protuberance, the nuchal ligament, the spinous process of the seventh cervical vertebra, and all the thoracic vertebrae. Its fibers are divided into upper, middle, and lower portions, which insert into the lateral third of the clavicle, the acromion, and the spine of the scapula, respectively.

• Upper Fibers: When contracted, the upper fibers elevate, upwardly rotate, and retract the scapula. This action is particularly noticeable when the shoulders are shrugged upwards.
• Middle Fibers: The contraction of the middle fibers primarily causes scapular retraction, drawing the shoulder blades together and upwardly rotating them.
• Lower Fibers: Often the most overlooked part of the trapezius, the lower fibers, when well-developed, contribute to the distinct "cobra" appearance. These fibers originate from the spine and insert into the scapula. They are responsible for depressing the scapula (pushing the shoulder blades downward), aiding in scapular adduction (bringing the shoulder blades closer together), and working in conjunction with the upper fibers to upwardly rotate the scapula.

When the attachment point closer to the head (the cranium or cervical vertebrae) is stabilized, contraction of the upper fibers results in elevation and upward rotation of the scapula, as well as retraction. With the distal attachment point stabilized (such as when the hands are fixed in position), unilateral contraction of the trapezius can cause the head to tilt towards the same side and rotate towards the opposite side, while bilateral contraction straightens the head and spine. Developing this muscle in children and adolescents can help prevent and correct postural issues like kyphosis (hunchback).