The presence of a large number of Type 1 muscle fibers (slow twitch or red muscle fibers that are rich in myoglobulin and carry more oxygen) in the erector spinae muscle group makes it resistant to fatigue.
A vital part of the human anatomy, muscles are soft tissues that facilitate locomotion. They allow us to change or maintain posture. The ability of the human spine to bend forward or backward, rotate, or twist, is attributed to several layers of muscles that support the back.
Erector spinae muscles, also referred to as the sacrospinal muscle group, is one such muscle group that primarily acts as an extensor. It consists of three muscles that help in extending the vertebral column. This muscle group runs from the base of the skull to the sacrum. Basically, it consists of three columns of muscles that are present on either side of the vertebral column. These are known as Iliocostalis, Longissimus, and Spinalis. Spinalis muscle lies closest to the vertebral column. It begins as a thick tendon from the sacrum and travels up. The longest of these three muscles, longissimus inserts at the mastoid process, which is the temporal process that is located behind the ear, at the base of the skull. Iliocostalis lies furthest from the vertebral column, and extends from the base of the skull to the pelvis.
Location of Erector Spinae Muscles
The erector spinae is one of the three true or intrinsic back muscles. It is this muscle group that allows the spine to return to erect position after bending. We bend backwards when these muscles contract, and when only the muscles on one side of the vertebral column contract, we are able to bend sideways. So, these muscles allow us to bend sideways, and facilitate the rotation of the spine and movement of the head. These help in maintaining the alignment of the spine.
Anatomy and Function of Erector Spinae Muscles
Arising from the angles of the third, fourth, fifth, and the sixth pair of ribs, Iliocostalis cervicis muscle inserts at the transverse process of the cervical vertebrae C4 to C6. This muscle helps in extending and hyperextending the cervical vertebrae. It also facilitates the lateral flexion of the cervical vertebrae.
Arising from the upper borders of the angles of the inferior six ribs (seventh to the twelfth pair of ribs), Iliocostalis thoracis muscle inserts into the upper borders of the angles of first to the sixth pair of ribs, and into the posterior transverse process of the C7, which is the seventh cervical vertebra. It helps in maintaining the erect posture of the spine
The insertion point of the iliocostalis lumborum are the inferior borders of the angles of the last pair of the true ribs (seventh rib), and the false and floating ribs, which means eighth to twelfth pair of ribs. It also inserts in the transverse processes of the first five lumbar vertebrae (L1-L5). This muscle plays a vital role in the extension of the vertebral column. When we bend forward, it provides resistance, and also helps in providing the force that is needed for bringing the body back to its normal, erect position. When we bend completely to touch our toes, these muscles are relaxed, while the load is on the ligaments, and on returning to the normal position, these muscles pass on the load to the hamstrings and the gluteus maximus, which is the outermost of the three gluteal muscles.
Arising from the transverse processes of the upper five thoracic vertebrae (T1 to T5), this muscle inserts in the transverse processes of the second to sixth cervical vertebrae. It helps in extending the cervical region of the vertebral column and maintaining the erect posture. It is also lends stability to the spinal column during flexion. When only the muscle on one of the sides is working, it helps in bending and rotating to that particular side.
It arises from the sacrum and medial iliac crest through the iliocostalis lumborum tendon and lumbosacral aponeurosis, and the transverse and spinous processes of vertebrae of the lumbar region. It inserts in the transverse processes of the thoracic vertebrae. It helps in extending the thoracic region or the lower vertebral column.
It arises from the transverse and the articular processes of the middle and lower cervical vertebrae (C4 or C5-C7), and the transverse processes of the upper thoracic vertebrae (T1-T5). It inserts into the posterior aspect of the mastoid process of the temporal bone. It helps extend the head and rotate it to the opposite side.
The function of the spinalis muscle is to extend the vertebral column, and laterally bend the neck and trunk.
This muscle arises from the spinous process of the lower thoracic vertebrae (T11) or lumbar vertebrae (L2-L3). It inserts into the spinous processes of the third to eight thoracic vertebrae. Its function is similar to that of the other erector spinae muscles, i.e., extension of the vertebral column. It also helps maintain erect posture. Also, it will help in bending and twisting to the same side.
This muscle arises from the lower ligamentum nuchae and the spinous processes of the sixth or seventh cervical vertebrae (sometimes first or second thoracic vertebrae). It inserts into the spinous processes of the axis, or sometimes the third or fourth cervical vertebrae.
This muscle arises from the spinous processes of the lower cervical vertebrae and upper thoracic vertebrae. The insertion points are between the superior and the inferior nuchal lines of the occipital bone at the base of the skull.
On a concluding note, erector spinae muscles are extremely essential for stabilizing or strengthening the back. Though these muscles are quite strong due to the presence of Type 1 fibers, excessive strain can have an adverse effect on them, thereby causing back pain.