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The abdominal external oblique muscle is one of the outermost abdominal muscles, extending from the lower half of the ribs around and down to the pelvis. The external oblique muscle is situated on the lateral and anterior parts of the abdomen. It is broad, thin, and irregularly quadrilateral. The abdominal internal oblique muscle, also known as the interior oblique, is an abdominal muscle in the abdominal wall that lies below the external oblique muscle and just above the transverse abdominal muscle. The internal oblique muscle functions similarly to the external oblique muscle, except it rotates ipsilaterally.
| Characteristics | Values |
|---|---|
| Type | External and internal abdominal oblique muscles |
| Location | External obliques: lateral and anterior parts of the abdomen; Internal obliques: underneath the external obliques on each side of the trunk |
| Size | External obliques: largest of the flat muscles; Internal obliques: thinner and smaller than external obliques |
| Shape | Broad, thin, and irregularly quadrilateral |
| Function | External obliques: pull the chest downwards, compress the abdominal cavity, ipsilateral side-bending, and contralateral rotation; Internal obliques: similar function to external obliques but with ipsilateral rotation |
| Blood Supply | Upper two-thirds: lower intercostal arteries; Lower third: deep circumflex iliac artery or iliolumbar artery |
| Nerve Supply | Upper two-thirds: lower intercostal nerves T7-T11 and subcostal nerve T12; Lower third: iliohypogastric L1 from lumbar plexus |
| Common Injuries | Abdominal strains, hernias, and oblique strain (common in baseball) |
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What You'll Learn
External abdominal oblique muscle anatomy
The external abdominal oblique muscle (also known as the external oblique muscle or exterior oblique) is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. It is situated on the lateral and anterior parts of the abdomen. The muscle is broad, thin, and irregularly quadrilateral, with its muscular portion occupying the side and its aponeurosis occupying the anterior wall of the abdomen.
The external abdominal oblique muscle originates from the external surfaces of the fifth to twelfth ribs (lower eight ribs). These digitations are arranged in an oblique line, with the upper digitations attached close to the cartilages of the corresponding ribs and the lowest attached to the apex of the cartilage of the last rib. From here, the muscle fibres fan out towards the midline and inferior margins of the abdomen. The most posterior fibres course almost vertically, while the remainder passes anteromedially.
The external abdominal oblique muscle has a variety of functions depending on whether it contracts unilaterally or bilaterally. When contracting unilaterally and in synergy with the contralateral internal abdominal oblique, it rotates the trunk to the opposite side. For example, the right external oblique would side-bend to the right and rotate to the left. Working together with the ipsilateral abdominal and back muscles, it also contributes to lateral flexion of the trunk on the same side. When contracting bilaterally, the muscle works together with the internal abdominal oblique and rectus abdominis to flex the trunk anteriorly. This activity increases the tone of the abdominal wall and intra-abdominal pressure, which is important for various physiological processes such as forced exhalation, micturition, defecation, and labour.
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 upper two-thirds of the muscle receive blood supply from the lower posterior intercostal and subcostal arteries, while the lower third is supplied by the deep circumflex iliac artery.
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External abdominal oblique muscle function
The external abdominal oblique muscle is one of the outermost abdominal muscles, situated on the lateral and anterior parts of the abdomen. It is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. Each side of the body has an external oblique muscle, which extends from the lower half of the ribs around and down to the pelvis.
The external abdominal oblique muscle has a variety of functions, depending on whether it contracts unilaterally or bilaterally. When acting unilaterally and in synergy with the contralateral internal abdominal oblique, it rotates the trunk to the opposite side. This is also referred to as flexion and contralateral rotation of the torso. The right external oblique would side-bend to the right and rotate to the left, and vice versa.
When contracting bilaterally with the internal abdominal oblique and rectus abdominis, the external abdominal oblique flexes the trunk anteriorly. This activity increases the tone of the abdominal wall and intra-abdominal pressure, which is a part of various physiological processes such as forced exhalation, micturition, defecation, and labour. Bilateral contraction of the external oblique 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 external abdominal oblique muscle also helps to stabilise the trunk and maintain consistent internal pressure in the abdomen. It helps to regulate pressure when there is a need for an increase, such as during essential bodily functions like breathing, coughing, vomiting, and childbirth.
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Internal abdominal oblique muscle anatomy
The internal abdominal oblique muscle is one of the five main abdominal muscles, the others being the pyramidalis, rectus abdominis, external oblique, and transversus abdominis. It is a part of the abdominal wall muscles, which help to stabilise the trunk and maintain normal abdominal tension. The internal abdominal oblique muscle lies on the lateral abdominal wall, comprising one of its three layers. It is situated below the external oblique muscle and above the transversus abdominis muscle. Its fibres run perpendicular to the external oblique muscle, beginning in the thoracolumbar fascia of the lower back, the anterior two-thirds of the iliac crest (upper part of the hip bone), and the lateral half of the inguinal ligament.
The internal abdominal oblique muscle has 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 typically arise from the lateral two-thirds of the superior surface of the inguinal ligament, forming a common attachment with the iliac fascia. 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 abdominal oblique muscle is involved in multiple actions. During unilateral contraction, it laterally flexes the trunk to the same side and rotates the trunk to the same side. During bilateral contraction, it flexes the trunk. It also compresses and provides structural support to adjacent abdominal structures and depresses the ribs at their costovertebral joints during forced expiration.
The internal abdominal oblique muscle is supplied by the lower intercostal nerves, as well as the iliohypogastric nerve and the ilioinguinal nerve. In males, some of the anterior fibres extend into the spermatic cord and form the cremaster muscle.
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Internal abdominal oblique muscle function
The internal abdominal oblique muscle is a thin, broad muscular sheet found on the lateral side of the abdomen. It is one of the three layers of the lateral abdominal wall, along with the external oblique and transversus abdominis muscles. The internal abdominal oblique is located just inside the hip bones, above the external oblique muscle.
The internal abdominal oblique muscle has several functions, including:
- Maintaining normal abdominal tension and increasing intra-abdominal pressure.
- Flexing the trunk when contracted bilaterally.
- Ipsilateral flexion and rotation of the trunk when contracted unilaterally.
- Working with the external oblique muscle to allow the trunk to twist and turn.
- Helping to protect the spine and keep the body stable and balanced.
- Holding internal organs in place and protecting them.
The internal abdominal oblique muscle is important for maintaining core stability and supporting the trunk during movement. Weakness in this muscle can increase the risk of abdominal hernias.
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Abdominal oblique muscle strain
The abdominal external oblique muscle is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. The external oblique is situated on the lateral and anterior parts of the abdomen. It is broad, thin, and irregularly quadrilateral, with its muscular portion occupying the side and its aponeurosis occupying the anterior wall of the abdomen. The abdominal internal oblique muscle sits directly next to the external oblique, closer to the core. These muscles work together when people twist or rotate their bodies at the core.
Abdominal muscle strain, or a pulled stomach muscle, is a common injury that can affect any abdominal muscle, including the obliques. It is caused by a stretch or tear in the muscle, often due to overuse or repetitive movements, especially in sports or other physical activities. The oblique strain is a common injury in baseball, particularly in pitchers, and can affect the leading side external oblique or the trailing internal oblique. It can also occur in other sports such as tennis, football, and golf, which involve a lot of reaching and side-to-side trunk movements.
The main signs of an abdominal muscle strain are abdominal pain and musculoskeletal pain. This pain may be felt during activities such as coughing, sneezing, laughing, sprinting, or vigorous exercise. It can also occur when getting up after a prolonged period of sitting or inactivity. Other symptoms include muscle spasms and stiff muscles. In the case of a severe strain, a person may experience a hernia, which can cause a lump or bulge at the site, as well as aching or burning. A hernia can also lead to constipation or nausea and vomiting.
To treat an abdominal muscle strain, rest, time, and appropriate treatments are necessary for recovery. Applying ice packs and warm compresses to the injured area can help reduce pain and inflammation. It is important to consult a healthcare provider for a proper diagnosis and to receive suggestions for lowering the risk of re-injury. Physical therapy can also be beneficial for recovery and improving pain in the obliques.
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Frequently asked questions
Abdominal obliques are the external and internal abdominal muscles that make up the lateral abdominal muscles. They are located on the sides of the abdominal wall.
The external abdominal oblique muscle is the outermost and largest of the three flat abdominal muscles. It helps pull the chest downwards, compressing the abdominal cavity and increasing intra-abdominal pressure. It also helps with side-bending and rotation of the trunk.
The internal abdominal oblique muscle is located underneath the external oblique muscle. It is thinner and smaller than the external oblique and works together with it to allow the trunk to twist and turn. It also helps to maintain internal abdominal pressure.
