Dominic Stone
The rotator muscles are a set of short muscles located laterally along the vertebral column, attaching between the transverse and spinous processes of the thoracic vertebrae. They are the deepest muscles in the transversospinalis group and are divided into rotatores cervicis, thoracis, and lumborum. The rotatores thoracis are the most developed and can be further subdivided into long and short rotatores. While the rotatores have minimal contribution to spine movements, they function as stabilizers of the vertebral column, acting as extensible ligaments that adjust their length to support adjacent vertebrae. They also play a role in fine-tuning vertebral motion and preventing damage to the facet joint capsules and the annulus of intervertebral discs. During ipsilateral trunk rotation, the muscle activity of the latissimus dorsi and external oblique is significantly increased.
| Characteristics | Values |
|---|---|
| Type of muscle | Rotatores muscles are the deepest muscles in the transversospinalis group, the deep layer of intrinsic back muscles. |
| Location | Rotatores muscles are located laterally along the vertebral column, attaching between the transverse and spinous processes of thoracic vertebrae. |
| Function | Rotatores muscles function as stabilizers, extensors and rotators of the spine. |
| Innervation | Rotatores muscles are innervated by the medial branches of posterior rami of spinal nerves. |
| Blood supply | Rotatores muscles receive arterial blood from the dorsal branches of posterior intercostal and lumbar arteries, arising from the supreme intercostal artery and thoracic aorta. |
| Subtypes | Rotatores muscles can be divided regionally into rotatores colli/cervicis, rotatores thoracis, and rotatores lumborum. |
| Development | Rotatores thoracis is the most developed subtype, while rotatores colli and lumborum are often inconsistent and can be replaced by deep fibers of the multifidus muscle. |
| Number of pairs | There are typically eleven pairs of rotatores muscles, but the first or last pair may sometimes be absent. |
| Length | Rotatores muscles can be further classified into long rotatores and short rotatores based on the length of their muscle fibers. |
| Attachment | Long rotators originate from the transverse processes of thoracic vertebrae and insert into the bases of spinous processes and laminae of vertebrae located two levels above. Short rotators have identical attachments but extend only one level above their origin. |
| Role in spinal movement | Rotatores muscles occupy positions of poor mechanical leverage, and their contribution to spine movements is minimal. Instead, they act as stabilizers of the vertebral column, functioning as extensible ligaments that adjust their length to support adjacent vertebrae. |
| Ipsilateral rotation | Ipsilateral rotation is associated with increased muscle activity in the internal oblique, transversus abdominis, and latissimus dorsi muscles. |
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What You'll Learn
Latissimus dorsi
The latissimus dorsi is a large, flat muscle that covers the back and stretches to the sides, behind the arm. The name "latissimus dorsi" comes from Latin and means "broadest [muscle] of the back". It is also the widest muscle in the human body.
The latissimus dorsi is responsible for several movements of the shoulder joint, including extension, adduction, transverse extension (also known as horizontal abduction or horizontal extension), flexion from an extended position, and internal rotation. It also assists in depression of the arm, along with the teres major and pectoralis major. When the arms are in a fixed overhead position, the latissimus dorsi pulls the trunk upward and forward.
The latissimus dorsi is also involved in the extension and lateral flexion of the lumbar spine, and it assists in forced expiration and as an accessory muscle of inspiration during deep inspiration and forceful respiratory functions such as coughing and sneezing.
The muscle is supplied by the thoracodorsal artery and receives innervation from the sixth, seventh, and eighth cervical nerves through the thoracodorsal nerve.
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External oblique
The external oblique is a large, thin, irregularly quadrilateral muscle that is the outermost of the three flat abdominal muscles of the lateral anterior abdomen. It is situated on the lateral and anterior parts of the abdomen, originating from the external surfaces of the lower eight ribs (ribs 5-12) and inserting into the iliac crest and the rectus sheath. The muscle fibres fan out towards the midline and inferior margins of the abdomen, with the most posterior fibres running almost vertically and the remainder passing anteromedially. The external oblique is supplied by the ventral branches of the lower six thoracoabdominal nerves and the subcostal nerve on each side. The cranial portion of the muscle is supplied by the lower intercostal arteries, while the caudal portion is supplied by branches of either the deep circumflex iliac artery or the iliolumbar artery.
The external oblique has a variety of functions, depending on whether it contracts unilaterally or bilaterally. When contracting unilaterally, the external oblique performs ipsilateral side-bending and contralateral rotation of the trunk. Specifically, it causes ipsilateral nutation by pulling the ilium posteriorly and rotating the rib cage down and towards the contralateral pelvis, increasing the ipsilateral lordosis. It also assists the contralateral internal oblique in inducing contralateral counternutation. When contracting bilaterally, the external oblique flexes the trunk anteriorly, increasing intra-abdominal pressure, which is useful in processes such as breathing, singing, and defecation.
The external oblique works synergistically with other muscles to produce movements of the spine and compress the abdominal viscera. When acting unilaterally, it works with the contralateral internal abdominal oblique to rotate the trunk to the opposite side. When contracting bilaterally, it works together with the internal abdominal oblique and rectus abdominis to flex the trunk anteriorly. Additionally, the external oblique contributes to the inguinal canal and forms the inguinal ligament.
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Internal oblique
The internal oblique is an abdominal muscle in the abdominal wall. It lies below the external oblique muscle and just above the transverse abdominal muscle. Its fibres run perpendicular to the external oblique muscle, beginning in the thoracolumbar fascia of the lower back, the anterior 2/3 of the iliac crest (upper part of the hip bone) and the lateral half of the inguinal ligament.
The internal oblique is referred to as a ""same-side rotator". It assists in respiration by compressing the abdominal wall during forced expiration. The internal and external obliques are collectively referred to as the obliques and work in tandem to carry out the same movements. However, the internal obliques are same-side rotators, while the external obliques are opposite-side rotators. For example, the left internal and external obliques contract for left lateral flexion, but the left internal oblique and right external oblique contract for left rotation.
The internal oblique is a local stabilizer of the lumbar vertebrae due to its origin on the lumbar fascia. Inhibition or lengthening of the muscle can contribute to poor core stability, increasing the risk of lower back injury. Overactive or short internal obliques can contribute to swayback posture and increase the chance of shoulder injury due to the restriction of overhead mobility associated with excessive kyphosis.
If the internal oblique on one side is inhibited or lengthened while the external oblique on the opposite side is inhibited or lengthened, the torso will bend laterally and rotate toward the side of the inhibited internal oblique.
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Transversus abdominis
The transversus abdominis is a broad, paired muscular sheet found on the lateral sides of the abdominal wall. It is also referred to as the transverse abdominis, transversalis muscle, and transverse abdominal muscle (TVA). The transversus abdominis is the innermost of the flat muscles of the abdomen. It is a deep muscle, layered below the internal oblique muscle.
The transversus abdominis has several origin points: the lateral one-third of the superior surface of the inguinal ligament and the associated iliac fascia; the anterior two-thirds of the inner lip of the iliac crest; the thoracolumbar fascia between the iliac crest and the 12th rib; and the internal aspects of the lower six ribs and their costal cartilages. From these origin points, the transversus abdominis fibres course horizontally over the lateral abdominal wall towards the midline, perpendicular to the linea alba.
The transversus abdominis helps to compress the ribs and viscera, providing thoracic and pelvic stability. It also assists in exhalation, contracting during the exhalation phase of respiration to force air out of the thorax. This muscle is vital for back and core health, and it helps to pull in what would otherwise be a protruding abdomen, earning it the nickname the "corset muscle".
Weak transversus abdominis muscles can result in abdominal pain. Typical signs of weakness in this muscle include toned abdominals above the navel but a bulge below it, an inability to hold in the stomach after a large meal or when gassy, and low back fatigue after prolonged standing or walking.
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Rectus abdominis
The rectus abdominis muscle, or "abdominal muscle", is a pair of segmented skeletal muscles on the front of a person's abdomen. It is commonly referred to as the "six-pack". The rectus abdominis is the top layer of abdominal muscles and is contained in the rectus sheath, a fibrous compartment that also contains the pyramidalis muscle. The rectus abdominis is a very long, flat muscle that extends along the whole length of the front of the abdomen.
The rectus abdominis is attached by two tendons: the larger one is attached to the pubic crest, from the pubic tubercle to the pectineal line, while the small, medial tendon is attached to the pubic symphysis. The muscle fibres then extend vertically superiorly and insert into the xiphoid process of the sternum and the costal cartilages of the 5th, 6th, and 7th ribs. The rectus abdominis is separated at the midline by a band of dense connective tissue called the linea alba, which is crossed by three fibrous bands called the tendinous intersections. These bands divide the muscle into segments, resulting in a six-pack shape in those with low body fat.
The rectus abdominis is an important postural muscle. It acts to flex the spinal column, tense the anterior wall of the abdomen, and assist in compressing the contents of the abdomen. It also assists with breathing and plays a role in respiration when forcefully exhaling, such as after exercise. The muscle is innervated by thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves. The blood supply to the rectus abdominis arises from a number of vessels, but predominantly the inferior and superior epigastric arteries.
To isolate the rectus abdominis during exercise, the knees should be bent to minimise the engagement of the hip flexors. The sit-up exercise is an example of a movement that targets the rectus abdominis, requiring the trunk to be raised against gravity to the midline and slowly lowered down repeatedly in multiple sets.
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Frequently asked questions
The latissimus dorsi, external oblique, internal oblique, and transversus abdominis muscles are involved in ipsilateral trunk rotation.
The LD and EO muscles must work together during ipsilateral trunk rotation to control upper trunk motions.
The IO and TrA muscles are activated early during ipsilateral trunk rotation at lumbar levels.
Ipsilateral neck flexion is caused by the longus colli, splenius capitis, and splenius cervicis muscles.
