Dominic Stone
The back muscles are organised into three main groups that run from the neck, down the spine to just above the hips. These muscles support the torso, enable movement, and assist in breathing. The erector spinae muscles, also known as the sacrospinalis muscle, are a group of longitudinal muscles that extend the length of the spine. They are covered by the thoracolumbar fascia in the thoracic and lumbar regions. The erector spinae can be divided into three groups: iliocostalis, longissimus, and spinalis. These groups are further divided into subdivisions based on the area of the spine they insert into, such as lumborum, thoracis, cervicis, and capitis.
| Characteristics | Values |
|---|---|
| Muscle Group | Extensor Muscles |
| Location | Attached to the back of the spine |
| Function | Allow us to stand and lift objects |
| Largest Muscles | Erector Spinae |
| Muscle Subdivision | Iliocostalis, Longissimus, Spinalis |
| Muscle Function | Extend and laterally flex the spine |
| Muscle Innervation | Lateral branches of the posterior primary divisions (dorsal rami) of spinal nerves |
| Muscle Coverage | Covered posteriorly by the thoracolumbar fascia |
| Muscle Layers | Three layers, with the posterior layer attaching to lumbar spinous processes |
| Muscle Development | Extend caudally, with origins inferior to insertions |
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What You'll Learn
Erector spinae muscles
The erector spinae muscles are a group of muscles that play a crucial role in spinal stability and movement. They are considered core and paraspinal muscles, forming the intermediate layer of the deep, intrinsic muscles of the back. These muscles extend along either side of the vertebral column, from the base of the cranium to the pelvis.
The erector spinae muscles are divided into three groups, known as iliocostalis, longissimus, and spinalis. The iliocostalis muscles are the most lateral part of the erector spinae. They originate from the sacrum, erector spinae aponeurosis, and iliac crest, and have several regional variations based on their insertions. The iliocostalis lumborum, for example, inserts into the 12th to 7th ribs.
The longissimus muscles are the central component of the erector spinae. They are divided into three regional groups, similar to the spinalis muscles. The longissimus capitis, for instance, originates from the transverse processes of vertebrae C4-T5 and inserts into the mastoid process of the temporal bone. The longissimus muscles share the same innervation as the spinalis muscles, receiving arterial blood from various arteries, including the vertebral and occipital arteries.
The spinalis muscles are the most medial erector spinae muscles. They are also divided into three regional groups, from superior to inferior. The spinalis capitis, for example, originates from the spinous processes of C7-T1 vertebrae and inserts into the occipital bone. The spinalis muscles function to extend and laterally flex the cervical and thoracic regions of the spine.
The erector spinae muscles have several important functions. They are responsible for moving the vertebral column, with bilateral contraction resulting in spine extension, while unilateral contraction causes lateral flexion. Additionally, these muscles help maintain posture by stabilising the lumbar spine and steadying the spine on the pelvis during walking.
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Multifidus muscles
The multifidus muscle is a long, narrow muscle that runs down both sides of the spine and is part of the transversospinal muscle group. It is composed of short, triangular muscles that, along with the semispinalis and rotatores, form the transversospinal group of deep back muscles. The multifidus is the thickest muscle in this group.
The multifidus muscle is divided into three regions: cervical multifidus, thoracic multifidus, and lumbar multifidus. Each muscle spans three to six vertebral levels, connecting the transverse and spinous processes of cervical, thoracic, and lumbar vertebrae. The cervical multifidus muscles, for instance, originate from the superior articular processes of C4–C7 vertebrae and extend to insert on the lateral aspect of the C2–C5 vertebrae.
The multifidus muscle has numerous attachment points, allowing each spinal bone (vertebra) to work individually and efficiently. It works in conjunction with the transversus abdominis and pelvic floor muscles to stabilize the lumbar spine, particularly during standing or movement. The multifidus helps to maintain spinal strength and stability, reducing spinal flexibility and rotation.
Bilateral contraction of the multifidus muscle results in the extension of the vertebral column at all levels. When the muscles contract unilaterally, they produce ipsilateral lateral flexion and contralateral rotation of the vertebral column. The multifidus also functions as extensible ligaments, adapting their length to stabilize the vertebrae and protect against spinal deterioration and arthritis.
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Latissimus dorsi muscles
The latissimus dorsi muscles, commonly referred to as the "'lats'", are large, flat muscles that cover the width of the middle and lower back. They are the largest muscles in the upper half of the body, starting below the shoulder blades and extending to the spine and hips. The name "latissimus dorsi" comes from Latin and means "broadest of the back".
The latissimus dorsi muscles play a crucial role in various movements of the body. They assist in the extension, adduction, transverse extension or horizontal abduction, flexion from an extended position, and internal rotation of the shoulder joint. Additionally, they are involved in the extension and lateral flexion of the lumbar spine. These muscles are responsible for connecting the spine to the humerus, and their tightness can contribute to chronic shoulder and back pain.
The latissimus dorsi muscles are frequently used during upper body exercises or movements that involve reaching the arms overhead or behind. Activities such as swimming, rowing, golfing, and weightlifting can strain these muscles if not properly warmed up or cooled down. Therefore, it is essential to practice proper form and technique during exercise to prevent injuries and strains.
Injuries to the latissimus dorsi muscles can cause pain and discomfort. Rest, ice, and over-the-counter anti-inflammatory medications can help alleviate pain and reduce inflammation. Consulting a healthcare professional, such as a doctor or physical therapist, is crucial for proper diagnosis and treatment. They can recommend specific exercises and stretches to strengthen the latissimus dorsi muscles and improve flexibility.
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Trapezius muscles
The trapezius muscles are two large muscles found on either side of the upper back. They are also referred to as "traps" or "trap muscles". Each trapezius muscle has three sections: the upper, middle, and lower sections. The upper section connects to the skull and neck (cervical spine), while the middle and lower sections attach to the bones in the thoracic spine.
The trapezius muscles start at the base of the neck and extend across the shoulders, forming a V shape down to the middle of the back. They are responsible for various functions, including maintaining and adjusting posture, turning the head, twisting the torso, shrugging the shoulders, and moving the shoulders and arms. The trapezius muscles work in conjunction with other muscles, such as the rhomboids, levator scapulae, serratus anterior, and deltoid, to produce coordinated movements and maintain proper shoulder mechanics.
The trapezius muscles are crucial for stabilizing and moving the scapula (shoulder blade). The upper fibres elevate the scapulae, the middle fibres retract them, and the lower fibres depress them. Additionally, the trapezius muscles induce scapular rotation, which is essential for a full range of motion during arm elevation and abduction.
Injury to the trapezius muscles can result in pain and dysfunction. Common causes of trapezius muscle pain include overuse, injuries, and nerve damage. Tearing or straining the trapezius is uncommon but can occur in bodybuilders lifting heavy weights or during high-velocity accidents. Dysfunction of the trapezius can lead to winged scapula or abnormal mobility and function of the scapula (scapular dyskinesia).
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Levator scapulae muscles
The levator scapulae is a long and slender muscle that belongs to the extrinsic muscles of the upper back. It is a posterior axio-appenducular muscle that connects the upper limb to the vertebral column and lies in the posterior triangle of the neck. The levator scapulae is innervated by the anterior rami of spinal nerves C3 and C4 and the dorsal scapular nerve (C5), a branch of the brachial plexus. The dorsal scapular artery is the predominant blood supply of the levator scapulae muscle.
The levator scapulae originates on the posterior tubercle of the transverse process of cervical vertebrae C1 to C4. The muscle fibres descend laterally to insert at the superior angle and medial border of the scapula, between the superior angle and base of the spine of the scapula. The superior third of the levator scapulae lies deep to the sternocleidomastoid, while the inferior third is deep to the trapezius.
The main function of the levator scapulae muscle is to elevate and retract the shoulder girdle at the scapulothoracic joint. It also helps prevent the depression of the girdle when carrying heavy loads. Additionally, the levator scapulae acts with the trapezius, latissimus dorsi, rhomboids, pectoralis major, and pectoralis minor muscles to inferiorly rotate the glenoid cavity, stabilize the spine, and extend and laterally flex the neck.
Bilateral contraction of the levator scapulae contributes to the extension of the cervical spine. A forward head posture puts increased tension on the levator scapulae muscles, which can lead to cervicogenic headaches. The most common clinical manifestation of levator scapulae pathology is levator scapulae syndrome or tenderness over the upper medial angle of the scapula. Effective treatment modalities include physical therapy and local corticosteroid injections.
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Frequently asked questions
The erector spinae muscles extend the spine. They are a group of longitudinal muscles that course the length of the spine.
The erector spinae can be divided into three groups: the iliocostalis, the longissimus, and the spinalis.
The latissimus dorsi, levator scapulae, rhomboids, and trapezius muscles all support the spine and torso.
