Here at Osmosis, we support each other - we’ve got each other’s backs. And it turns out, our backs support all of us! Let’s look at the muscles of the back that help maintain our posture and also provide movements of the trunk and upper limb.

The muscles of the back are divided into two major groups: the extrinsic back muscles and the intrinsic back muscles. The extrinsic back muscles include the superficial back muscles, which produce and control upper limb movements, and the intermediate back muscles, which are thought to be involved in respiratory movements.

The superficial extrinsic back muscles include the trapezius, latissimus dorsi, levator scapulae, and the two rhomboids - rhomboid major and rhomboid minor.

All these muscles are posterior axioappendicular muscles, which connect the axial skeleton, primarily the vertebral column, to the superior appendicular skeleton, specifically the pectoral girdle and the humerus.

The posterior axioappendicular group is divided into two subgroups. The first subgroup consists of two superficial muscles: the trapezius and latissimus dorsi.

The trapezius is a large triangular muscle that covers the posterior aspect of the neck and the superior half of the back. There are two trapezius muscles in the back, which when seen together, look like a trapezium.

Proximally, the trapezius originates on the medial third of the superior nuchal line, the external occipital protuberance, the nuchal ligament, and the spinous processes of the C7 to T12 vertebrae.

Distally, the trapezius inserts on the lateral third of the clavicle, the acromion, and the spine of the scapula. Based on the orientation of its fibers, the trapezius is divided into the descending - or superior - part, the middle part, and the ascending - or inferior - part.

Contraction of the descending part results in elevation of the scapula, like when shrugging the shoulders. Contraction of the middle part retracts the scapula, and contraction of the ascending part depresses the scapula, lowering the shoulder.