Anatomy of Extrinsic Back Muscles

The extrinsic back muscles help control arm movements, and they also play a role in breathing. These muscles include a set of superficial extrinsic back muscles and a set of intermediate extrinsic back muscles. This article describes the structure and function of the superficial layer of the extrinsic back muscles.

Function of the Superficial Extrinsic Back Muscles

Extrinsic back muscles are one of two main sets of spinal extensor muscles. The other set is the intrinsic back muscles. Extrinsic and intrinsic back muscles are grouped according to their location and their function.

Both extrinsic and intrinsic back muscles are necessary for spinal support because most of our weight is in front of us. The powerful muscles located in the back maintain upright posture and support trunk movement.

The extrinsic back muscles are located towards the outside of the body.

They are divided into two groups:

• The superficial extrinsic back muscles
• The intermediate extrinsic back muscles

The hallmark of the superficial layer is in controlling arm movements. Breathing is also greatly influenced by the intermediate extrinsic layer.

Muscles of the Superficial Extrinsic Group

The superficial extrinsic back muscle group is comprised of 4 muscles: The trapezius, latissimus dorsi, levator scapula, and the rhomboids.

Trapezius Muscle

One of the most notable features of the trapezius muscle is its shape. The trapezius (called “traps” for short) is a large trapezoid-shaped muscle.

This muscle has a number of functions:

• Moving the shoulder blades
• Contributing to head and neck motions
• Assisting with breathing

The muscle is located at the mid and upper back, and at the neck and shoulders. The trapezius muscle has 3 parts: The upper, middle and lower.

Latissimus Dorsi

A triangularly shaped muscle, the latissimus dorsi, often referred to as "lats", is a key player when you use your arms to pull your body weight. For this reason, it is often referred to as the “swimmer's muscle.” The lats assist with breathing, too.

The lats take up a good amount of space in the low and mid-back. They start at the bottom of the thoracic spine and ribs, the thoracolumbar fascia and part of your hip bone. They then taper into a fine point that inserts on the inside of the upper arm bone.

Levator Scapula

The levator scapula muscle lifts the shoulder blade up toward the ears. When this action is constantly “on” it can result in lots of neck and shoulder tension.

The muscle starts at the neck and travels down to attach on the medial corner of the top of the shoulder blade.

Rhomboids

The rhomboid muscles are two parallelogram-shaped muscles (right and left) that extend from the midline of the spine to the inner border of the scapula (shoulder blade bone).

Each rhomboid consists of a major and minor part called the rhomboid major and the rhomboid minor. Though two separate structures, the major and minor, make one overall shape and act as a unit to squeeze the shoulder blades together. They also provide additional motions and actions.

Because of its action of squeezing the shoulder blades together, the rhomboids can be targeted for posture improvement exercises. The action of squeezing the shoulder blades together (towards the spine) may help reverse the effects of sitting at the computer and/or other forms of postural kyphosis.