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The spine is a complex structure of 26 interconnected bones, known as vertebrae, that allow for a range of movements, including twisting, bending, and arching. The muscles that power spinal rotation differ depending on the region of the spine. In the lower back, the internal and external oblique abdominal muscles are primarily responsible for rotation, while intrinsic muscles such as the multifidus and longissimus contribute to this movement. The multifidus, in particular, helps control spinal twisting by contracting on one side and extending the lumbar spine when contracted on both sides. The latissimus dorsi and external oblique muscles also play a role in spinal rotation, with increased activity during ipsilateral rotation at thoracic vertebral levels. Additionally, the erector spinae and transversospinalis groups, including the semispinalis, rotatores, and multifidus, contribute to spinal rotation, particularly during unilateral movement. Weakened muscles can decrease support for spinal movements and increase the risk of injuries, especially during activities involving heavy lifting or shovelling.
| Characteristics | Values |
|---|---|
| Muscles responsible for spinal rotation | Internal oblique abdominals, external oblique abdominals, multifidus, longissimus, latissimus dorsi, rectus abdominis, internal oblique, transversus abdominis, serratus posterior superior, serratus posterior inferior, erector spinae, splenius cervicis, splenius capitis, and transversospinalis |
| Muscles responsible for spinal extension | Semispinalis, rotatores, multifidus, erector spinae, splenius cervicis, splenius capitis, and transversospinalis |
| Muscles responsible for spinal flexion | Rhomboids, serratus posterior superior, serratus posterior inferior, levator scapulae, erector spinae, and transversospinalis |
| Muscles responsible for spinal lateral flexion | Erector spinae, splenius cervicis, splenius capitis, and transversospinalis |
| Muscle groups in the back | Extrinsic and intrinsic |
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What You'll Learn
The multifidus and longissimus muscles
The longissimus muscles, also known as longissimus thoracis, are part of the lumbar erector spinae. They originate at the dorsal aspect of each lumbar transverse process and attach to the medial aspect of the posterior superior iliac spine. These muscles are believed to counteract lumbar flexion and derotate the spine. Together with the iliocostalis fibers, the longissimus muscles form an aponeurosis that serves as an indirect connection between the lumbar vertebrae and the ilium.
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The internal and external oblique abdominal muscles
The internal oblique is a thin muscular sheet found on the lateral side of the abdomen, underneath the external oblique. It is one of three layers of the lateral abdominal wall, along with the external oblique and transversus abdominis. The internal oblique is important for movements of the trunk and increasing intra-abdominal pressure. Weakness in the oblique abdominal muscles can impair the range of motion of the trunk and affect spinal movements.
Healthy spine rotation is important for preventing injuries, as rotated vertebrae or a "twisted spine" can result from certain movements or underlying conditions. While the spine can move in many directions, there are limits to how far it should twist, especially when bending forward or lifting heavy objects, as this can increase the risk of back injuries such as strains and herniated discs.
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The latissimus dorsi muscle
The latissimus dorsi is a large, flat muscle that covers the majority of the lower posterior thorax. It is a broad muscle that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The name "latissimus dorsi" comes from Latin and means "broadest of the back". The muscle is also referred to as "lats", especially among bodybuilders.
The latissimus dorsi is an extrinsic muscle of the back, meaning it originates from the myogenic cells in the developing upper limb buds. It is supplied predominantly by the thoracodorsal artery, a continuation of the subscapular artery, which is a branch of the third part of the axillary artery. The muscle also receives blood supply from the dorsal perforating branches of the inferior three posterior intercostal arteries and the superior three lumbar arteries.
The latissimus dorsi is responsible for extension, adduction, transverse extension (also known as horizontal abduction or horizontal extension), flexion from an extended position, and internal rotation of the shoulder joint. It also plays a role in the extension and lateral flexion of the lumbar spine. The muscle assists in holding the scapula against the thorax during upper limb movements and can pull the inferior angle of the scapula in various directions, producing movements on the shoulder joint.
The latissimus dorsi works collaboratively with the teres major and pectoralis major muscles to perform actions of the upper extremity, including adduction, medial rotation, and extension of the arm at the glenohumeral joint. It is also active in moving the trunk forward and upward when the upper extremities are fixed overhead, as in climbing or performing a chin-up. Research has shown that the muscle is active during deep inspiration and forceful respiratory functions such as coughing and sneezing.
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The erector spinae and transversospinalis muscles
Erector Spinae Muscles
The erector spinae muscles form the intermediate layer of the deep intrinsic muscles of the back. They extend along either side of the vertebral column, from the base of the skull to the pelvis. These muscles are responsible for extending and laterally flexing the spine, head, and neck. The erector spinae muscles are divided into three groups, from medial to lateral: spinalis, longissimus, and iliocostalis.
The spinalis muscles are the most medial erector spinae muscles and are innervated by the posterior rami of cervical, thoracic, and lumbar spinal nerves. They are divided into three regional groups: spinalis capitis, spinalis colli, and spinalis thoracis. These muscles function to extend and laterally flex the cervical and thoracic regions of the spine.
The longissimus muscles are the central and thickest erector spinae muscles. They are divided into three groups, similar to the spinalis muscles: longissimus capitis, longissimus colli, and longissimus thoracis. The longissimus muscles function to extend and laterally flex the spine and also help rotate the head.
The iliocostalis muscles are the most lateral erector spinae muscles and are divided into three groups: iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis. Their function is associated with the lateral position, and tightness in these muscles can affect the position of the hips and rib cage.
Transversospinalis Muscles
The transversospinalis muscles are part of the deep layer of back muscles and are responsible for extension, lateral flexion, and rotation of the head and spine. These muscles contribute to the stability and movement of the spine, working in conjunction with the erector spinae muscles to facilitate spinal rotation and maintain posture.
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The semispinalis capitus muscle
The semispinalis capitus is a long, slender muscle that is part of the deep layer of muscles in the back. It is the superior and largest component of the three-part semispinalis muscle, which also includes the semispinalis cervicis and semispinalis thoracis. The semispinalis capitus is situated at the upper and back part of the neck, deep to the splenius muscles and medial to the longissimus cervicis and longissimus capitis.
The semispinalis capitus originates on the articular processes of the C5, C6, C7, and C8 vertebrae, as well as the transverse processes of T1-T6. It attaches to the occiput between the superior and inferior nuchal lines. This muscle is innervated by the dorsal rami of the cervical spinal nerves.
The semispinalis capitus is involved in extension, lateral flexion, and rotation of the head, cervical spine, and thoracic spine. It provides a long moment arm, allowing for efficient extension of the spine.
Together with the multifidus and rotatores muscles, the semispinalis group comprises the deep transversospinal layer of the back muscles. These intrinsic muscles are supplied by the posterior rami of spinal nerves. The semispinalis muscles have the longest fascicles within this group, spanning six segments.
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Frequently asked questions
The internal oblique abdominals and the external oblique abdominals are the muscles primarily responsible for powering spinal rotation in the lower back. The multifidus and longissimus also contribute to this twisting movement.
The multifidus helps the spine twist when one side is contracted (activated) and extends the lumbar spine when both sides contract. It is also the largest muscle of the lumbar spine.
The spinal column is made of 26 interconnected bones, called vertebrae. Rotated or twisted vertebrae, especially when bending forward, are associated with a risk of back injuries like strain and herniated disc.
Weakened muscles may decrease support for any spinal movement, including twisting. Muscle weakness can also diminish overall trunk stability.
