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The human spine is a flexible column that is capable of flexion, extension, lateral flexion, and rotation. The muscles of the spine work like guy ropes to control and prevent the spine from falling in a particular direction. The lumbar spine, for example, is responsible for most spinal flexion below the neck, with the psoas minor muscle playing a key role in flexing the trunk at the spinal joints. Additionally, the erector spinae, a group of muscles in the trunk and pelvis, also contribute to flexion, along with other muscles such as the rectus abdominis, external and internal oblique abdominal muscles, and the psoas major. Understanding the specific muscles involved in spinal movement is crucial for developing effective conditioning exercises and maintaining spinal health.
| Characteristics | Values |
|---|---|
| Major muscles involved | Rectus abdominis, external and internal oblique, erector spinae, semispinalis thoracis, latissimus dorsi, deep posterior spinal muscles, quadratus lumborum, and psoas |
| Muscle groups | Erector spinae, Transversospinalis |
| Muscle fibres | Vertical or oblique |
| Muscle function | Flexion, extension, lateral flexion, and rotation |
| Muscle actions | Contract to control or prevent the falling of the spine |
| Muscle movement | Flexion is the most pronounced spinal motion |
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What You'll Learn
- The psoas minor flexes the trunk at the spinal joints
- The rectus abdominis, external oblique abdominal muscles, and internal oblique abdominal muscles
- The erector spinae, composed of three subgroups: iliocostalis, longissimus, and spinalis
- The multifidus and rotatores of the transversospinalis group
- The diaphragm attaches to the internal surfaces of the sternum, lower six ribs, and costal cartilages
The psoas minor flexes the trunk at the spinal joints
The psoas muscle is a core muscle that plays a crucial role in the body's functional and dynamic movements. It is a long, ribbon-shaped muscle that runs along the spine, connecting the upper and lower body. There are two types of psoas muscles: the psoas major and the psoas minor. While the psoas major is present in most individuals, the psoas minor is found in two out of three people, and its absence does not cause any health issues.
The psoas minor is a small muscle that sits on top of the psoas major. It originates from the upper section of the psoas major and connects to the iliopsoas muscle in the pelvis. The iliopsoas muscle is formed by the combination of the psoas muscle and the iliacus muscle. This muscle group is essential for hip flexion and movement, helping us walk and climb stairs.
The psoas minor muscle plays a specific role in flexing the trunk at the spinal joints. It enables the trunk to bend laterally, contributing to our ability to twist and turn our upper body. Additionally, it is involved in the posterior tilt of the pelvis at the lumbosacral joint, which is crucial for maintaining balance and stability.
Maintaining the health of the psoas minor is important for overall spinal health and stability. Tightness or inflammation in this muscle can cause pain and discomfort in the lower back and hips. Therefore, it is essential to include stretching and warming up in one's routine to prevent injuries and maintain flexibility.
In summary, the psoas minor is a vital muscle that contributes to the flexibility and stability of the trunk at the spinal joints. Its functions include flexing the trunk, tilting the pelvis, and supporting spinal health. Understanding the role of the psoas minor can help promote overall well-being and prevent lower back issues.
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The rectus abdominis, external oblique abdominal muscles, and internal oblique abdominal muscles
The rectus abdominis is a pair of flat and parallel muscles that make up the top layer of the abdominal muscles, often referred to as the "'six-pack." It originates from the pubic crest and inserts with the help of fibers to the costal cartilage and the xiphoid process of the sternum. The rectus abdominis acts to flex the spinal column, tense the anterior wall of the abdomen, and assist in compressing its contents.
The external oblique abdominal muscles are large and sit on the top surface of the abdomen, extending from the lower ribs down to the pelvis. They cover the sides of the abdominal area, sitting just below the subcutaneous fat and skin. The external obliques contribute to a variety of trunk movements, including flexion and rotation. Bilateral contraction of the external obliques, along with the rectus abdominis and internal oblique, flexes the trunk by drawing the pubis towards the xiphoid, as in crunches or sit-ups.
The internal oblique abdominal muscles lie underneath the external obliques on each side of the trunk. It is a broad, sheet-like muscle that originates from the inguinal ligament, iliac crest, and lumbodorsal fascia, inserting onto ribs 10-12. Bilateral contraction of the internal oblique compresses the abdomen, while unilateral contraction ipsilaterally rotates the torso.
Weak abdominal muscles can lead to spinal problems, so it is important to maintain core stability through exercises that target these muscle groups, such as sit-ups and crunches.
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The erector spinae, composed of three subgroups: iliocostalis, longissimus, and spinalis
The spine is capable of flexion, extension, lateral flexion, and rotation. To understand the muscles that produce a given movement of the spine, it can be helpful to think of the spine as a flexible column with the muscles acting like guy ropes. When the vertebral column leans off the vertical, the muscles opposite to the direction in which the spine is leaning must contract to control or prevent the falling of the spine in that direction. Muscles of the spine are also often used together in a coordinated manner to create a stable desired position of the spine.
The erector spinae is a group of muscles and tendons that run the length of the spine on the left and right, from the sacrum and hips to the base of the skull. They are also known as the sacrospinalis group of muscles. These muscles lie on either side of the spinous processes of the vertebrae and extend throughout the lumbar, thoracic, and cervical regions. The erector spinae is composed of three subgroups: iliocostalis, longissimus, and spinalis.
The iliocostalis muscles are the most lateral erector spinae muscles. They are attached to the ribs. According to their attachments and location, they are regionally divided into three groups, from superior to inferior: Iliocostalis colli muscle originates from the angle of ribs 3 to 6 and inserts into the transverse processes of vertebrae C4-C6. The function of the iliocostalis muscle is to extend and laterally flex (ipsilateral) the spine.
The longissimus muscles are the central erector spinae muscles. They are also the thickest and the longest. The longissimus muscles are divided into three regional groups, from superior to inferior: Longissimus capitis muscle originates from the transverse processes of vertebrae C4-T5 and inserts into the mastoid process of the temporal bone; Longissimus colli muscle extends between the transverse processes of vertebrae T1-T5 and transverse processes of vertebrae C2-C6; and longissimus thoracis originates from the sacrum, spinous processes of the lumbar vertebrae, and transverse process of the last thoracic vertebra and inserts in the transverse processes of the lumbar vertebrae, erector spinae aponeurosis, ribs, and costal processes of the thoracic vertebrae. The function of the longissimus muscles is to extend and laterally flex (ipsilateral) the spine. Longissimus capitis also helps to rotate the head ipsilaterally.
The spinalis muscles are the most medial erector spinae muscles. They are divided into three regional groups, from superior to inferior: Spinalis capitis muscle originates from the spinous processes of C7-T1 vertebrae and inserts into the midline of the occipital bone; Spinalis cervicis is an inconstant muscle fibre that runs from the cervical and upper thoracic and then inserts in the external occipital protuberance. The function of the spinalis muscles is to extend and laterally flex the cervical and thoracic regions of the spine.
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The multifidus and rotatores of the transversospinalis group
The multifidus and rotatores are part of the transversospinalis group, a deep layer of intrinsic back muscles that lie between the transverse and spinous processes. These muscles are small and have a poor mechanical advantage for contributing to motion. They include the three semispinalis muscles, the multifidus muscle, and the rotatores muscles.
The multifidus is the largest muscle of the lumbar spine and lies deep to the semispinalis. It spans the whole length of the vertebral column and is most developed in the lumbar region. The multifidus attaches from the sacrum and PSIS and the mammillary processes of the lumbar spine and transverse processes of the thoracic spine to the spinous processes of vertebral segments.
The rotatores are the deepest muscles in the transversospinalis group and have the shortest fascicles, spanning one to two segments. They consist of two parts: the long (longus) and short (brevis) rotatores. The rotatores attach from the transverse processes of the lumbar and thoracic spine to vertebral segments one to two levels superior to the inferior attachment.
The transversospinalis group functions in spinal stability, proprioception, and posture, stabilizing the vertebral column. They share the same nerve supply from the dorsal rami of the spinal nerves. As a group, the transversospinalis extends, laterally flexes, and contralaterally rotates the trunk at the spinal joints.
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The diaphragm attaches to the internal surfaces of the sternum, lower six ribs, and costal cartilages
The diaphragm is a dome-shaped muscle and tendon that functions as the main muscle of respiration. It is located at the inferior-most aspect of the rib cage, filling the inferior thoracic aperture. It acts as the floor of the thoracic cavity and the roof of the abdominal cavity. The diaphragm is composed of two distinct muscle regions: the costal, which serves as the driver in the work of breathing, and the crural diaphragm, which serves as an "anchor" by attaching the muscle to the lower ribs and lumbar vertebrae.
The diaphragm attaches to the internal surfaces of the sternum, the lower six ribs, and their costal cartilages, and L1-L3. The muscle fibres from these attachments converge in a central tendon, which forms the crest of the dome. The diaphragm increases the volume of the thoracic cavity by its central dome dropping down and/or by pulling the rib cage attachment up.
The diaphragm's peripheral part consists of muscular fibres that originate from the circumference of the inferior thoracic aperture and converge to be inserted into a central tendon. The diaphragm's superior origin is continuous from the xiphoid process anteriorly to the lower six costal cartilages of the thorax laterally and the first two lumbar vertebrae posteriorly. The right crus arises from L1-L3 vertebral bodies and their intervertebral discs, while the smaller left crus arises from L1-L2 vertebral bodies and their intervertebral discs.
The diaphragm undergoes contraction and relaxation, altering the volume of the thoracic cavity and the lungs, producing inspiration and expiration. During inhalation, the diaphragm contracts and moves inferiorly, enlarging the volume of the thoracic cavity and reducing intra-thoracic pressure, allowing the lungs to expand. When the diaphragm relaxes and moves in the superior direction, air is exhaled by the elastic recoil process of the lung and the tissues lining the thoracic cavity.
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Frequently asked questions
Spinal flexion involves the spinal flexors, including the rectus abdominis, external oblique abdominal muscles, internal oblique abdominal muscles, and psoas major.
The spinal flexors are responsible for flexing the spine or posteriorly tilting the pelvis against gravity or external resistance.
Yes, exercises such as the curl-up, curl-back, pelvic tilt, and hip lift involve spinal flexion. These exercises can help improve spinal alignment issues.
