The trapezius is a large diamond shaped muscle on your back that runs from the base of your skull, out to your shoulder, and down your thoracic spine. This muscle is easy to palpate as it is the most superficial of your posterior muscles. We use our trapezius for movements such as shrugging, rowing, and reaching up overhead.
Because the trapezius has a broad range of actions, some of which oppose each other, this muscle is anatomically broken down into three parts: upper, middle, and lower.
The upper muscle fibers of the trapezius originate from posterior aspects of the skull and neck: superior nuchal line (medial third), occipital protuberance (external), and the ligamentum nuchae (posterior neck ligaments). They insert onto the clavicle (lateral third). The upper trapezius extends, laterally flexes, and rotates the head and neck, along with elevating and upwardly rotating the scapula. A muscle with similar action is the levator scapula.
The middle muscle fibers of the trapezius orginate from the spinous processes of C-7 through T-3. They insert onto the acromion process and the spine of the scapula (superior). The middle trapezius adducts the scapula (shoulder retraction), stabilizes the scapula, and performs a small amount of upward rotation and elevation of the scapula. Muscles with a similar action are the rhomboids.
The origin sites for the lower muscle fibers of the trapezius are the T4 – T12 spinous processes. These fibers then insert themselves onto the middle and inferior portion of scapular spine. The lower trapezius depresses and upwardly rotates the scapula. It does adduct the scapula some as well. With the origin site on the thoracic spine, the lower trapezius can also act as a weak spinal extensor when the insertion site is fixed. A muscle with similar action is the serratus anterior.
I remember when I became intrigued by the trapezius muscle. It was during my upper level anatomy course in college – Human Dissection. The cadaver I was assigned to was a petite elderly lady. During one of the first days of lab, my professor asked us to begin dissecting away the skin and adipose layers of the mid to upper region of the back to expose the trapezius muscle. My lab partner and I went carefully to work at the lower regions of the thoracic spine. While we were dissecting away the yellow adipose tissue we began to comment that the adipose tissue was looking a little bit odd, linear in appearance. We continued to remove this tissue away expecting to find the lower trapezius muscle underneath. It was a bit surprising to find rhomboid major and latissimus dorsi instead. What my partner and I soon learned was that the linear shaped adipose tissue we removed was actually the lower fibers of the trapezius muscle which had been transformed through a process called fatty infiltration. This elderly lady apparently had some type of degenerative disorder, such as severe kyphosis, that prevented her from being able to use her lower trapezius muscle to pull her shoulders down and back or upwardly rotate her scapula for overhead reaches. Because of her inability to contract these lower fibers, they were eventually converted into fat. The upper muscle fibers of her trapezius were normal.
In my next post I’ll give you a Yoga Tune Up® pose to help keep your whole trapezius healthy and happy!