Dominic Stone
The abdominal muscles are essential for supporting the trunk, allowing movement, and holding organs in place by regulating internal abdominal pressure. The deep abdominal muscles, together with muscles in the back, make up the core muscles, which help keep the body stable and balanced while protecting the spine. The torso muscles are also crucial for longitudinal rotation between the upper and lower torso, and twisting the trunk involves the contraction of internal and external oblique muscles.
| Characteristics | Values |
|---|---|
| Number of abdominal muscles | 5 |
| Location of abdominal muscles | Between the ribs and the pelvis on the front of the body |
| Function of abdominal muscles | Hold internal organs in place, support the trunk, allow movement, regulate internal abdominal pressure |
| Core muscles | Include transversus abdominis, pelvic floor muscles, oblique muscles, multifidus, and muscles in the back |
| Function of external obliques | Allow the trunk to twist from side to side |
| Function of internal obliques | Work with external obliques to allow the trunk to twist and turn |
| Function of transversus abdominis | Stabilize the trunk and maintain internal abdominal pressure |
| Function of back muscles | Support the torso, enable movement, help with breathing |
| Back muscle groups | Latissimus dorsi, levator scapulae, rhomboids, trapezius, serratus anterior |
| Prevention of abdominal muscle strain | Regular stretching, warming up before exercise, cooling down afterward, maintaining good form during sports |
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What You'll Learn
Internal and external obliques
The internal and external obliques are two of the five main abdominal muscles, the others being the pyramidalis, rectus abdominis, and transversus abdominis. The abdominal muscles are strong bands of muscles lining the walls of the abdomen (or trunk) and are located between the ribs and the pelvis on the front of the body. They support the trunk, allow movement, and hold internal organs in place by regulating internal abdominal pressure.
The internal obliques are a pair of muscles on top of the external obliques, just inside the hip bones. They are much thinner and smaller than the external obliques. Like the external obliques, they are on the sides of the rectus abdominis, running from the sides of the trunk towards the middle. The internal obliques originate on the inguinal ligament, which is a ligament that runs from the anterior iliac spine to the pubic bone. They insert onto the costal cartilages of the lower four ribs and the abdominal aponeurosis, which is a superficial sheet of connective tissue over the abdomen. They also insert on the linea alba, which is a fibrous band of connective tissue that runs from the xiphoid process to the pubic symphysis.
The external obliques are a pair of muscles, one on each side of the rectus abdominis. They are the largest of the flat muscles and sit at the bottom of the stack. They run from the sides of the body towards the middle. The external obliques originate on the lower eight ribs. They insert onto the abdominal aponeurosis, the linea alba, the iliac crest, and the pubic bone.
The internal and external obliques work together to allow the trunk to twist and turn. For example, twisting the trunk to the left requires the left side internal oblique and the right side external oblique to contract together. They can also function independently: the internal obliques can function bilaterally, meaning both sides work together, or unilaterally, meaning one-sided. The external obliques function bilaterally to flex the trunk and compress its contents, and unilaterally to flex the trunk and rotate the trunk to the opposite side.
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Transversus abdominis
The transversus abdominis is a deep abdominal muscle that is layered below the internal oblique muscle. It is the deepest of the flat muscles, and is found on the lateral sides of the abdominal wall. It is one of the four main abdominal muscle groups, and is the deepest muscle layer.
The transversus abdominis is important for maintaining normal abdominal tension and increasing intra-abdominal pressure. It helps to stabilise the trunk, and maintain internal abdominal pressure. It also assists in exhalation, and compresses the ribs and viscera to provide thoracic and pelvic stability.
The transversus abdominis works with the segmental stabilisers of the spine, such as the multifidi, to increase spine stability and protect against back injury or strain during movement or normal posture. It is also important for back and core health, and can help to prevent low back pain.
Weakness in the transversus abdominis can lead to a protruding abdomen, and low back fatigue after prolonged standing or walking.
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Erector spinae
The erector spinae is a large, superficial muscle that lies just deep to the thoracolumbar fascia and arises from the erector spinae aponeurosis (ESA). It is one of the core and paraspinal muscles and plays an important role in spinal stability. The erector spinae is formed of three muscles with its fibres running vertically throughout the lumbar, thoracic, and cervical regions. It lies in the groove to the side of the vertebral column.
The erector spinae is divided into three groups, from medial to lateral: spinalis, longissimus, and iliocostalis. The spinalis muscles are the most medial erector spinae muscles and are responsible for extending and laterally flexing the cervical and thoracic regions of the spine. They are divided into three regional groups: spinalis capitis, spinalis colli, and spinalis thoracis. The longissimus muscles are the central erector spinae muscles and are also the thickest and longest. They are divided into three regional groups: longissimus capitis, longissimus colli, and longissimus thoracis. The longissimus muscles function to extend and laterally flex the spine and help rotate the head. The iliocostalis muscles are the most lateral erector spinae muscles and are also divided into three groups: iliocostalis cervicis, iliocostalis thoracis, and iliocostalis lumborum.
The erector spinae muscles are responsible for moving the vertebral column. Bilateral contraction of these muscles extends the spine, while unilateral contraction causes lateral flexion. They also help maintain posture by steadying the spine on the pelvis during walking. In individuals with low back pain, the erector spinae flexion-relaxation phenomenon is absent. Lumbar stabilization exercises can help restore this phenomenon and decrease low back pain.
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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 of the back". The muscle is commonly referred to as "lats", especially in bodybuilding circles.
The latissimus dorsi is the widest muscle in the human body. It is relatively thin and covers almost all back muscles at the posterior trunk, except the trapezius. It is attached to the dorsal vertebrae, with the number of vertebrae varying from four to eight. The muscle is also attached to the costal cartilage of the ribs. The latissimus dorsi crosses the inferior angle of the scapula and is involved in the movement of the scapulae, such as their downward rotation.
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 medial internal rotation. It also plays a role in the extension and lateral flexion of the lumbar spine. When the arms are in a fixed overhead position, the latissimus dorsi pulls the trunk upward and forward, as in climbing or performing a chin-up.
The muscle is innervated by the sixth, seventh, and eighth cervical nerves through the thoracodorsal nerve. It receives its blood supply primarily from the thoracodorsal artery, a branch of the subscapular artery, as well as from the dorsal perforating branches of the posterior intercostal and lumbar arteries.
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Multifidus
The multifidus is a group of short, triangular muscles that form the transversospinales muscles group along with the semispinalis and rotatores. The multifidus muscle is located in the third or deep layer of deep muscles of the back, running through the groove between the spinous and transverse processes of vertebrae. It is found on either side of the vertebral column, extending from the cervical to the lumbar spine.
The multifidus is an important stabilizer of the lumbar spine, working with the transversus abdominis and pelvic floor muscles to stabilize the spine. It spans the whole length of the vertebral column but is most developed in the lumbar area. When contracting bilaterally, the multifidus extends the spine, while unilateral contraction produces lateral flexion of the spine to the same side and rotation of the spine to the opposite side.
The multifidus has a high cross-section area, giving it a high force-generating capacity, and a low fibre length, resulting in a low muscle excursion. Investigators have categorized multifidus fibre types by layers, with the deepest layer contributing more strength and stability to the spine than the superficial layers. This is possibly due to the deep layer having a shorter "excursion", meaning that when the muscle contracts, it contributes to more compression-type motion at the spinal joint.
Weakness and atrophy in the multifidus muscle are associated with chronic low back pain. Persistent lumbar multifidus dysfunction is diagnosed by the atrophic replacement of the multifidus with fat, as visualized by magnetic resonance imaging or ultrasound. One way to strengthen the lumbar multifidus muscles is by tensing the pelvic floor muscles for a few seconds, similar to stopping urination midstream.
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Frequently asked questions
The internal and external oblique muscles are responsible for twisting the torso.
The internal oblique muscles are located just inside the hipbones. They work in opposition to the external oblique muscles.
The external oblique muscles are the largest of the flat muscles and sit at the bottom of the stack. They run from the sides of the body toward the middle.
The abdominal muscles, including the transversus abdominis, rectus abdominis, and multifidus, along with muscles in the back, make up the core muscles and help move the trunk.
You can strengthen your torso twisting muscles by incorporating exercises that target your core muscles, such as Pilates, bridging, and modified bridging.
