Muscles are cordlike structures, they can stretch and have the ability to contract, or shorten. This is, in fact, what happens when you lift a cup of coffee, throw a ball, or do anything that requires movement of the body. The muscles shorten and lengthen, pulling the bones in different directions to coordinate our movements. When you lift, lower, push, pull, carry, or perform any activity, the muscles are doing the work. Muscles also work to keep the body from moving when movement is not desired. For example, if you are sitting in a canoe and the canoe starts to tip to the left, your muscles quickly respond by coordinating your body’s movement to the right to maintain your balance.
Muscles are true workhorses and can be your back’s best friend. When conditioned, your muscles maintain their strength, endurance, and flexibility, which allows the body to move and work with less risk of injury and pain. When working properly, the muscles can greatly reduce the load on the bones, facet joints, disks, and ligaments. In contrast, when the muscles become deconditioned from lack of use or from injury, they tend to lose their size, strength, endurance, and flexibility and can also be painful! Back muscles, like any other muscle in the body, require adequate exercise to maintain strength and tone.
While muscles like the gluteals (in the thighs) are used any time we walk or climb a step, deep back muscles and abdominal muscles are usually left inactive and unconditioned. Unless muscles are specifically exercised, back muscles and abdominal muscles tend to weaken with age.
The three types of back muscles that help the spine function are extensors, flexors and obliques.
To treat back pain in the lower spine and lower back, always focus on strengthening the flexor, extensor and oblique muscles to help reinforce support of the spine and in turn, reducing low back pain and sometimes even eliminating the pain.
Extensor, Flexor and Oblique Muscles
- The extensor muscles are attached to the posterior (back) of the spine and enable standing and lifting objects. These muscles include the large paired muscles in the lower back (erector spinae), which help hold up the spine, and gluteal muscles.
- The flexor muscles are attached to the anterior (front) of the spine (which includes the abdominal muscles) and enable flexing, bending forward, lifting, and arching the lower back.
- The oblique muscles are attached to the sides of the spine and help rotate the spine and maintain proper posture.
There is a large and complex group of muscles that work together to support the spine, help hold the body upright and allow the trunk of the body to move, twist and bend in many directions. Back muscles are divided into two specific groups: the extrinsic muscles that are associated with upper extremity and shoulder movement, and the intrinsic muscles that deal with movements of the vertebral column. Several small muscles in the cervical area of the vertebral column are also important.
The Extrinsic Muscles
Superficial extrinsic muscles connect your upper extremities to the trunk, and they form the V-shaped musculature associated with the middle and upper back. They include the trapezius, latissimus dorsi, levator scapulae, and the rhomboids. Intermediate extrinsic muscles include the serratus posterior superior and inferior. Most of their function is involved with respiration.
The Intrinsic Muscles
Intrinsic muscles, which stretch all the way from the pelvis to the cranium, help to maintain your posture and move the vertebral column. They’re divided into three groups: the superficial layer, the intermediate layer, and the deep layer. The muscles in all of the layers are innervated by the posterior rami of spinal nerves. Injuries of the intrinsic back muscles often occur while using improper lifting technique. You can protect the back muscles by bending from the hip and knee when you lift objects from the ground.
The Superficial Layer
Muscles originating from the vertebral column and having their fleshy bellies located in the back, but inserting onto the appendicular skeleton of the upper limb or the ribs. They are not innervated by dorsal primary rami of spinal nerves, as are the deep or true muscles of the back. The superficial extrinsic back muscle group is comprised of 4 muscles: The trapezius, latissiumus dorsi, levator scapula and the rhomboids.
One of the most notable features of the trapezius muscle is its shape. The trapezius (called “traps” for short) is a large triangular shaped muscle located at the mid and upper back, and at the neck and shoulders. This muscle has a number of functions, not the least of which involves moving the shoulder blades (these are the flat – also triangularly shaped – bones that sit on the back of the ribcage.) Other functions of the trapezius includes contributing to head and neck motions, and assisting with breathing.
Another triangularly shaped muscle, the latissimus dorsi, 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 latissiumus dorsi is also called the “lats” for short.) The lats assist with breathing, too. The lats are take up a goodly 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.
The levator scapula muscle starts at the neck and travels down to attach on the media corner of the top of the shoulder blade. Its job is to lift the shoulder blade up toward the ears. This action is unfortunately constantly “on” for most of us, which can result in lots of neck and shoulder tension.
The rhomboid muscles are two paralleogram 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, respectively 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. Because of its action (of squeezing the shoulder blades together), targeting the rhomboids for posture improvement exercise may be a good idea. 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.
The teres major is a small, yet important muscle within the back. It is located underneath the lats, and has adopted the nickname, “The Little Lat.” As you might imagine, the teres major works in conjuction with the lats. But it also works with the rotator cuff muscles. Its functions include pulling the arms downwards and rotating them inwards.
The Intermediate Layer
This massive muscle forms a prominent bulge on each side of the vertebral column. It lies within a fascial compartment between the posterior and anterior layers of the thoracolumbar fascia. The common origin of the three columns is though a broad tendon that is attached inferiorly to the posterior part of the iliac crest, the posterior aspect of the sacrum, the sacroiliac ligaments, and the sacral and inferior lumbar spinous processes. This large muscle originates near the sacrum and extends vertically up the length of the back. It lies on each side of the vertebral column and extends alongside the lumbar, thoracic and cervical sections of the spine. The erector spinae functions to straighten the back and provides for side-to-side rotation. An injury or strain to this muscle may cause back spasms and pain. The erector spinae is arranged in three vertical columns: iliocostalis (lateral column); longissimus (intermediate column); and spinalis (medial column).
The iliocostalis is the muscle immediately lateral to the longissimus that is the nearest to the furrow that separates the epaxial muscles from the hypaxial. It lies very deep to the fleshy portion of the serratus ventralis (serratus anterior). The iliocostalis originates from the sacrum, erector spinae aponeurosis and iliac crest. The iliocostalis has three different insertions according to the parts.
The iliocostalis cervicis (cervicalis ascendens) arises from the angles of the third, fourth, fifth, and sixth ribs, and is inserted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrae.
The iliocostalis dorsi (musculus accessorius; iliocostalis thoracis) arises by flattened tendons from the upper borders of the angles of the lower six ribs medial to the tendons of insertion of the iliocostalis lumborum; these become muscular, and are inserted into the upper borders of the angles of the upper six ribs and into the back of the transverse process of the seventh cervical vertebra.
The iliocostalis lumborum (iliocostalis muscle; sacrolumbalis muscle) is inserted, by six or seven flattened tendons, into the inferior borders of the angles of the lower six or seven ribs.
The longissimus is the muscle lateral to the semispinalis. It is the longest subdivision of the sacrospinalis that extends forward into the transverse processes of the posterior cervical vertebrae. The longissimus muscle has three parts with different origin and insertion.
The longissimus thoracis is the intermediate and largest of the continuations of the sacrospinalis.
In the lumbar region, where it is as yet blended with the iliocostalis lumborum, some of its fibers are attached to the whole length of the posterior surfaces of the transverse processes and the accessory processes of the lumbar vertebræ, and to the anterior layer of the lumbodorsal fascia.
In the thoracic region, it is inserted, by rounded tendons, into the tips of the transverse processes of all the thoracic vertebræ, and by fleshy processes into the lower nine or ten ribs between their tubercles and angles.
The longissimus cervicis (transversalis cervicis), situated medial to the longissimus dorsi, arises by long, thin tendons from the summits of the transverse processes of the upper four or five thoracic vertebræ, and is inserted by similar tendons into the posterior tubercles of the transverse processes of the cervical vertebrae from the second to the sixth inclusive.
The longissimus capitis (trachelomastoid muscle) lies medial to the longissimus cervicis, between it and the semispinalis capitis.
It arises by tendons from the transverse processes of the upper four or five thoracic vertebræ, and the articular processes of the lower three or four cervical vertebrae, and is inserted into the posterior margin of the mastoid process, beneath the splenius capitis and sternocleidomastoideus.
It is almost always crossed by a tendinous intersection near its insertion.
The spinalis is a portion of the erector spinae, a bundle of muscles and tendons, located nearest to the spine. It is divided into three parts: Spinalis dorsi, spinalis cervicis, and spinalis capitis. The spinalis muscle has three parts.
Spinalis dorsi, the medial continuation of the sacrospinalis, is scarcely separable as a distinct muscle. It is situated at the medial side of the longissimus dorsi, and is intimately blended with it; it arises by three or four tendons from the spinous processes of the first two lumbar and the last two thoracic vertebrae: these, uniting, form a small muscle which is inserted by separate tendons into the spinous processes of the upper thoracic vertebrae, the number varying from four to eight. It’s intimately united with the semispinalis dorsi, situated beneath it.
Spinalis cervicis, or spinalis colli, is an inconstant muscle, which arises from the lower part of the ligamentum nuchæ, the spinous process of the seventh cervical, and sometimes from the spinous processes of the first and second thoracic vertebrae, and is inserted into the spinosus process of the axis, and occasionally into the spinous processes of the two cervical vertebrae below it.
Spinalis capitis (biventer cervicis) is usually inseparably connected with the semispinalis capitis.
Iliocostalis muscle A muscle part of the erector spinae muscle group which helps to extend the spine (bend backwards).
The Deep Layer
Underneath the intermediate intrinsic back muscles is another layer of muscles that help to support posture and assist the intermediate muscles in moving the spine. The deep intrinsic muscles are smaller than the erector spinae muscles, and none of them traverse more than six vertebral segments.
This group is the most superficial of the deep intrinsic muscles. These muscles run from the midthoracic spine superiorly through the cervical spine. They have three divisions (thoracis, cervicis, and capitis) that originate from the transverse processes of the 4th cervical vertebra through the 10th, 11th, or 12th thoracic vertebra. The fibers travel superiorly for about four to six segments each and attach on spinous processes and the occipital bone.
The semispinalis dorsi (or semispinalis thoracis) consists of thin, narrow, fleshy fasciculi, interposed between tendons of considerable length. It arises by a series of small tendons from the transverse processes of the sixth to the tenth thoracic vertebrae, and is inserted, by tendons, into the spinous processes of the upper four thoracic and lower two cervical vertebrae.
The semispinalis cervicis (semispinalis colli), arises by a series of tendinous and fleshy fibers from the transverse processes of the upper five or six thoracic vertebrae, and is inserted into the cervical spinous processes, from the axis to the fifth inclusive. The fasciculus connected with the axis is the largest, and is chiefly muscular in structure. The semispinalis cervicis is thicker than the semispinalis dorsi.
The semispinalis capitis (complexus) is situated at the upper and back part of the neck, deep to the splenius, and medial to the longissimus cervicis and capitis. It is part of the transversospinales muscle group. It arises by a series of tendons from the tips of the transverse processes of the upper six or seven thoracic and the seventh cervical vertebrae, and from the articular processes of the three cervical vertebrae above this (C4-C6). The tendons, uniting, form a broad muscle, which passes upward, and is inserted between the superior and inferior nuchal lines of the occipital bone. It lies deep to the trapezius muscle and can be palpated as firm round muscle mass just lateral to the cervical spinous processes. The semispinalis muscles are innervated by the dorsal rami of the cervical spinal nerves.
Multifidus is a series of small muscles which travel up the length of the spine. These short, triangular muscles originate in various places but always travel superiorly and medially for two to four segments and attach on the spinous processes. The multifidus consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the vertebrae, from the sacrum to the axis. Each fasciculus, passes obliquely upward and medialward to insert into the whole length of the spinous process of one of the vertebrae above. The fasciculi vary in length: the most superficial, the longest, pass from one vertebra to the third or fourth above; those next in order run from one vertebra to the second or third above; while the deepest connect two contiguous vertebrae.
The rotatores lie underneath the multifidus muscles. They originate from the transverse processes of a single vertebra and travel superiorly to insert into the spinous process of the vertebra one or two segments superior to it. The rotatores help with rotation and proprioception.
External oblique abdominal muscles One of the powerful rotator muscles of the spine whose fibers run obliquely to the long axis of the body. Contribute to spinal movement by compressing the stomach organs and flexing the spine.
Internal oblique abdominal muscles One of the rotator muscles of the spine whose fibers run obliquely to the long axis of the body. Contribute to spinal movement by compressing the stomach organs and flexing the spine.
Rectus abdominis muscle A muscle that contributes to spinal movement by compressing the stomach organs and flexing the spine.
The Suboccipital Muscles
The suboccipital region includes the posterior part of the 2nd cervical vertebra to the area inferior to the occipital region of the head. Four small muscles located on each side of the suboccipital region help with posture and assist with extension and rotation of the head.
Rectus capitis posterior muscles: These two muscles insert onto the occipital bone; the rectus capitis posterior major originates at the spinous process of the 2nd cervical vertebra (the axis) and the rectus capitis posterior minor originates from the posterior arch of the 1st cervical vertebra (the atlas).
Obliquus muscles: These two muscles complete the suboccipital quartet. The obliquus capitis inferior travels from the spinous process of the 2nd cervical vertebra to the transverse process of the 1st cervical vertebra, and the obliquus capitis superior has its origin at the transverse process of the 1st cervical vertebra and inserts onto the occipital bone.