The Anatomy of the Muscles of the Back

Your back consists of a complex array of bones, discs, nerves, joints, and muscles. The muscles of your back support your spine, attach your pelvis and shoulders to your trunk, and provide mobility and stability to your trunk and spine.

The anatomy of your back muscles can be complex. There are several different layers of muscles in your back that are often pulling in different and various directions.

Understanding the anatomy and function of your back muscles can help you determine if (and when) you may need professional medical care if you are having a problem with your back.

Anatomy of Back Muscles

Your back consists of three distinct layers of muscles, namely the superficial layer, the intermediate layer, and the deep layer. These layers of back muscles help to mobilize and stabilize your trunk during your day to day activities. They also attach your shoulders and pelvis to the trunk, creating a bridge between your upper body and lower body.

The Superficial Layer

The superficial layer of back muscles lies just below your skin and fascia. Many of these muscles are easily identified and located simply by looking at and palpating your body. Superficial back muscles include:

Trapezius

The trapezius is divided into three distinct parts: the upper, middle, and lower trapezius. This muscle originates from your cervical spine and skull and from the spinous processes of cervical level seven through thoracic 12.

The flat, triangular-shaped muscle then courses along the back of your shoulder blade to attach to your clavicle, acromion, and spine of your scapula. Innervation of the trapezius is from the spinal accessory nerve, which is cranial nerve XI.

Rhomboid Major and Minor

Your rhomboids originate from the spinous process of cervical seven through thoracic five. They then attach to the medial border of your scapula. Innervation of the rhomboids is via the dorsal scapular nerve.

Latissimus Dorsi

Your "lats" are a major back muscle and mover of your shoulder joint. They originate from the thoracolumbar fascia, the spinous process of thoracic six through 12, the iliac crest, and your lower three ribs. The muscle then courses up to your shoulder and attaches to your upper arm bone. Innervation of the latissimus is via the thoracodorsal nerve.

The Intermediate Layer

The intermediate layer of back muscles includes the serratus posterior superior and inferior. These muscles course from your vertebral column to your ribs and assist your diaphragm and intercostal muscles in moving the ribs during breathing.

Serratus posterior superior originates from cervical seven through thoracic three and courses out to ribs two through five. The inferior serratus posterior originates from thoracic 11 through lumbar level three and attaches at ribs nine through 12. Both serratus posterior muscles are innervated by the intercostal nerves.

The Deep Layer

The deep layer of back muscles are also known as the intrinsic layer and reside closest to your spine. The deep layer consists of:

Erector Spinae

The erector spinae are long strap muscles that are made up of the iliocostalis, spinalis, and longissimus muscles. These muscles originate from the common tendinous origin of the iliac crest, sacrum, lumbar vertebrae, and sacroiliac and supraspinous ligaments.

They then travel up the length of your spine and insert on the ribs, transverse processes of the vertebrae, and the skull. Innervation of the erector spinae is via the posterior rami of the spinal nerves.

Multifidus

Your multifidus muscles originate from your sacrum, iliac spine, lumbar vertebrae, and transverse processes of thoracic and cervical vertebrae. Each bundle of fibers ascends two to four vertebral levels, attaching on the spinous process above. Multifidus muscles are innervated by the posterior rami of spinal nerves.

Quadratus Lumborum

Your quadratus lumborum, or QL, is the deepest back muscle and originates from your iliac crest and insert on the transverse process of lumbar one through five and the lower part of your twelfth rib. Innervation of the QL is via the twelfth thoracic nerve and the spinal rami of the lumbar nerves.

Each muscle in the deep, intermediate, and superficial layer come in pairs; there is one on the left and one on the right side of your body.

Function

The function of your back muscles varies depending on the specific muscle and the direction of pull of each muscle. Many of the muscles work together; one muscle may provide movement to a joint while a neighboring muscle provides stability.

For example, the function of your latissimus dorsi is to extend your shoulder, pulling it backward. While this is happening, your middle and lower trapezius contracts to stabilize your shoulder blade.

Each individual muscle or muscle group in your back serves a distinct function. These functions include:

• Trapezius: Your traps serve to elevate your shoulders. The middle and lower trapezius function to retract your shoulders, pulling them backward.
• Rhomboids: The rhomboids serve to retract and stabilize your shoulder blades.
• Latissimus dorsi: Your latissimus functions to extend and medially rotate your upper arm bone. They also help stabilize your low back when your arm is in a fixed weight-bearing position.
• Erector spinae: The erector spinae muscles extend your spine, bending it backward. When acting on one side only they serve to laterally flex your trunk.
• Multifidus: Each level of the multifidus muscle serves to stabilize the spinal segment to which it attaches.
• Quadratus lumborum: Your QL laterally flexes your spine when contracting on one side. If both quadratus lumborum muscles contract, extension of your spine occurs.

As stated earlier, the serratus posterior superior and inferior aid in moving the ribs during breathing.

Associated Conditions

Your back muscles work by stabilizing and moving your spine, trunk, and shoulders. Common problems with the muscles of your back or conditions that can cause muscular back pain may include:

• Back strain
• Back spasms
• Fatigue from poor posture or overexertion
• Disc herniation or degeneration
• Spinal arthritis
• Spondylolisthesis
• Sciatica

Many problems with your back muscles cause pain or spasm, and most conditions resolve with rest, over-the-counter medicine, and gentle stretches.

If you are having intense pain that prevents you from moving or if you experience weakness, numbness, or tingling in your leg or legs, it is recommended you visit your physician. They can examine you and determine the best course of treatment for your back problem.

Rehabilitation

Most episodes of back pain or spasm are short-lived and resolve with conservative measures. If you have injured your back muscles, you may benefit from working with a physical therapist to help you fully recover. Your therapist can assess your back muscles and determine what treatments are needed for your condition. Treatments may include:

• Stretching exercises: Exercises to elongate and stretch your back muscles may include the knees to chest stretch or the prayer stretch. These stretches can improve the flexibility and mobility of your spine, providing for more freedom of motion.
• Strengthening exercises: Keeping your back muscles strong can help you recover from back injuries and may prevent future problems with your back. Back strengthening exercises may include the reverse fly, the prone superman, or prone hip extension.
• Massage: Massage has been shown to improve local blood flow to injured back muscles and may increase tissue extensibility, leading to improved back motion.
• Heat or ice: Heat or ice is often used for back muscle strains to improve blood flow and decrease pain.
• Taping: Your physical therapist may apply kinesiology tape to your back muscles to provide biofeedback about back muscle positioning. The tape can also support your spine, making it easier for your muscles to keep you in an upright posture.
• Electrical stimulation: Electrical stimulation, like transcutaneous electrical neuromuscular stimulation (TENS), may be used to decrease pain and spasm in your back muscles after injury.

If your muscular back pain lasts for more than four weeks, you may need to have more advanced diagnostic studies like an X-ray or magnetic resonance imaging (MRI) to determine the underlying cause of your pain. These diagnostic tests show the bony and soft tissue anatomy of your spine and surrounding tissues.

Severe problems like sciatica or nerve root compression may require more invasive procedures like steroid injections or spinal surgery. The need for these procedures is rare; most episodes of back pain respond well to more conservative treatments.