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The abdominal muscles, commonly known as abs, are strong bands of muscles lining the walls of the abdomen, which is the trunk of the body. They are located at the front of the body, between the rib cage and the pelvis. The abdominal muscles are divided into four groups: the external obliques, the internal obliques, the transversus abdominis, and the rectus abdominis. These muscles have several important roles, including supporting the trunk, facilitating movement, and holding organs in place.
| Characteristics | Values |
|---|---|
| Location | Between the ribcage and pelvis at the front of the body |
| Function | Holding organs in place, supporting the trunk, allowing movement, maintaining posture, stabilising the trunk, maintaining internal abdominal pressure, protecting the spine, and controlling breathing |
| Composition | 5 main muscles: pyramidalis, rectus abdominus, external obliques, internal obliques, and transversus abdominis |
| Appearance | May form bumps or a ["six-pack"] when well-defined |
| Strains | Caused by overstretching, overuse, quick twisting of the trunk, improper technique in sports, lifting heavy objects, laughing, coughing, or sneezing |
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What You'll Learn
The rectus abdominis muscle
Strains of the rectus abdominis muscle can occur due to overstretching, improper technique during physical activity, or violent movements such as coughing, laughing, or sneezing. A rectus sheath hematoma, an accumulation of blood in the sheath of the muscle, can be caused by a rupture of the epigastric artery or a muscular tear. This condition can be serious and is becoming more common with the increasing use of anticoagulant medications in the ageing population.
To isolate the rectus abdominis muscle during exercise, one can perform a sit-up exercise or raise the trunk while bending the knees to minimise the engagement of hip flexors.
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External oblique muscles
The external oblique muscles are a pair of muscles located on the lateral sides of the abdominal wall. They are the largest and most superficial of the flat abdominal wall muscles. The external obliques are situated at the bottom of the stack of three flat muscles, with the internal obliques and transversus abdominis above them.
The external obliques originate from the external surfaces of ribs 5–12 and extend around and down to the pelvis. They cover the sides of the abdominal area, sitting on the top surface of the abdomen, right below the subcutaneous fat and skin. The muscle fibres fan out towards the midline and inferior margins of the abdomen, with the most posterior fibres running almost vertically.
The external oblique muscles allow the trunk to twist and turn. For example, when the right external oblique contracts, the body turns to the left. They work with the internal oblique muscles, which operate in the opposite way. So, to twist the trunk to the left, the left side internal oblique and the right side external oblique contract together.
The external oblique muscles also contribute to the lateral part of the abdominal wall. Their aponeurotic part contributes to the anterior abdominal wall, forming part of the anterior layer of the rectus sheath. The superior, medial, and inferior margins of the muscle relate to their respective attachment points, while the posterior margin is free.
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Internal oblique muscles
The abdominal muscles are strong bands of muscles lining the walls of the abdomen. They are located between the rib cage and the pelvis on the front of the body. The abdominal muscles have several important functions, including holding internal organs in place, supporting the trunk, and helping with movement.
The internal oblique muscles are a pair of muscles that flank the rectus abdominis and are located just inside the hip bones. They are much thinner and smaller than the external oblique muscles. Like the external oblique muscles, they are on the sides of the rectus abdominis, running from the sides of the trunk toward the middle. The internal oblique muscles are one of the three layers of the lateral abdominal wall. They are found deep to the external abdominal oblique and superficial to the transverse abdominis. The internal abdominal oblique is a broad, thin muscular sheet found on the lateral side of the abdomen.
The internal oblique muscles have multiple sites of origin, which are distributed along the anterolateral side of the trunk. According to their origin, the muscle fibres can be divided into the anterior, lateral, and posterior fibres. Anterior fibres arise from a deeper structure known as the iliopectineal arch. The fibres pass inferomedially, arching over the inguinal canal and merging with the tendinous fibres of the transversus abdominis muscle to form the conjoint tendon. Lateral fibres originate from the anterior two-thirds of the iliac crest and then diverge superiorly and medially. The fibres then extend into an aponeurosis that contributes to the formation of the rectus sheath and inserts at the linea alba. Posterior fibres originate from the posterior end of the iliac crest and the thoracolumbar fascia. The fibres then ascend superolaterally and insert into the inferior borders and tips of the lower three or four ribs and their cartilages.
The internal oblique muscles work with the external oblique muscles to allow the trunk to twist and turn. When the torso flexes and rotates, the internal oblique and the external oblique contract together. For example, twisting the trunk to the left requires the left side internal oblique and the right side external oblique to contract together. The internal oblique muscles are also accessory muscles of respiration, acting as antagonists to the diaphragm and helping to reduce the volume of the chest cavity during exhalation. When the internal obliques contract, they compress the organs of the abdomen, pushing them up into the diaphragm, which intrudes back into the chest cavity, reducing the volume of the air-filled lungs and producing an exhalation.
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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 the deepest layer of the lateral abdominal wall, lying beneath the internal and external abdominal oblique muscles. The transversus abdominis is one of the core muscles, attaching to the spine or pelvis.
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, oriented perpendicular to the linea alba.
The transversus abdominis is important for maintaining normal abdominal tension and increasing intra-abdominal pressure. It helps to stabilise the trunk and spine, and maintain internal abdominal pressure. It also serves to compress and retain the contents of the abdomen, providing thoracic and pelvic stability. The transversus abdominis also assists in exhalation, contracting during the exhalation phase of respiration to force air out of the thorax.
Weak transversus abdominis muscles can result in abdominal pain and an inability to hold in the stomach after a large meal or when gassy. The drawing-in technique is an effective way to strengthen the transversus abdominis.
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Pyramidalis
The pyramidalis muscle is a small, triangular-shaped muscle that is part of the abdominal wall. It is located at the base of the pubic bone and sits in front of the rectus abdominis, attaching to the linea alba. The linea alba is a line that divides the rectus abdominis into two segments.
The pyramidalis is a vertical muscle that is contained in the rectus sheath, a multilayered fascial compartment composed of the aponeuroses of the external abdominal oblique, internal abdominal oblique, and transversus abdominis muscles. The muscle originates from the pubic symphysis and pubic crest, with the bony attachment arising from tendinous fibres. The muscle belly narrows down as it courses superiorly and ends by inserting into the linea alba, midway between the umbilicus and pubis.
The pyramidalis muscle is innervated by the subcostal nerve, which is the anterior ramus of spinal nerve T12. The inferior and superior epigastric arteries supply blood to the muscle.
The pyramidalis muscle is present in about 80% of the population, although it may be absent in some individuals or unilateral, and the muscles on each side may be of unequal size. It is a vestigial muscle, meaning it is tendinous or reduced in size compared to homologous muscles in other species. The pyramidalis is thought to contribute to abdominal wall functions, such as increasing intra-abdominal pressure, and plays a role in protecting the abdominal organs and supporting physiological processes such as respiration, singing, micturition, and defecation.
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Frequently asked questions
Abdominal muscles are strong bands of muscles lining the walls of your abdomen (the trunk of your body). They support your trunk, help with movement, and hold your organs in place.
The abdominal muscles are located between your rib cage and pelvis on the front of your body.
The abdominal muscles can be broadly divided into anterolateral and posterior walls. The anterolateral abdominal wall muscles consist of two vertical muscles (rectus abdominis) and three flat muscles (external oblique, internal oblique, and transversus abdominis).
The rectus abdominis muscle helps hold internal organs in place, keeps the body stable during movement, and can form the appearance of a "six-pack" when well-defined.
You can strengthen your abdominal muscles by performing specific exercises such as rectus exercises and oblique exercises. It is recommended to consult a qualified fitness instructor or a healthcare professional for guidance on developing a safe and effective exercise program.
