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The abdominal external oblique muscle is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. The abdominal internal oblique muscle lies below the external oblique muscle and just above the transverse abdominal muscle. The internal and external obliques are a pair of muscles on each side of the rectus abdominis, which runs down the middle of the abdomen. The obliques work together to allow the trunk to twist and turn.
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What You'll Learn
External abdominal oblique anatomy
The external abdominal oblique muscle 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. 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 external oblique muscles are not visible in most humans due to subcutaneous fat deposits and their small size.
The external abdominal oblique is a paired muscle, with one on each side of the rectus abdominis. It is located in the anterolateral abdominal wall, extending from the lower half of the ribs around and down to the pelvis. The muscle originates from the external surfaces of ribs 5–12, with its fibres fanning out towards the midline and inferior margins of the abdomen. The most posterior fibres course almost vertically, while the remainder passes anteromedially.
The upper two-thirds of the external abdominal oblique are supplied by the lower intercostal nerves T7–T11 and the subcostal nerve T12. The lower third is supplied by the iliohypogastric L1 from the lumbar plexus. The upper two-thirds receive blood supply from branches of the lower posterior intercostal and subcostal arteries, while the lower third receives blood supply from the deep circumflex iliac artery.
The external abdominal oblique has various functions depending on whether it contracts unilaterally or bilaterally. When contracting unilaterally, it causes ipsilateral lateral flexion of the trunk and contralateral rotation of the trunk. When unilateral contraction is paired with the contraction of the internal abdominal oblique from the opposite side, it produces rotation of the trunk to the opposite side. Bilateral contraction, on the other hand, flexes the trunk anteriorly, increasing intra-abdominal pressure. This pressure increase is useful in processes such as breathing, singing, and defecation.
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Internal abdominal oblique anatomy
The internal abdominal oblique muscle is an abdominal muscle in the abdominal wall that lies below the external oblique muscle and just above the transverse abdominal muscle. It is a thin, flat muscle that is part of three layers of muscle in the lateral abdominal wall. It is found deep to the external abdominal oblique and superficial to the transverse abdominis.
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. The lateral fibres of the internal abdominal oblique muscle are continuous with the rectus sheath, the large aponeurosis of the anterior abdominal wall. The rectus sheath largely encloses the rectus abdominis and pyramidalis muscles, as well as many neurovascular structures of the anterior abdominal wall.
The internal abdominal oblique muscle 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 muscle fibres run from these points superomedially (up and towards the midline) to the muscle's insertions on the inferior borders of the 10th to 12th ribs and the linea alba. In males, the cremaster muscle is also attached to the internal oblique.
The internal abdominal oblique muscle performs two major functions. Firstly, as an accessory muscle of respiration, it acts as an antagonist to the diaphragm, helping to reduce the volume of the chest cavity during exhalation. When the diaphragm contracts, it pulls the lower wall of the chest cavity down, increasing the volume of the lungs, which then fill with air. Conversely, 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. Secondly, its contraction causes ipsilateral rotation and side-bending. It acts with the external oblique muscle on the opposite side to achieve this torsional movement of the trunk. For example, the right internal oblique and the left external oblique contract as the torso flexes and rotates to bring the left shoulder towards the right hip.
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Function of the abdominal oblique muscles
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 external abdominal oblique muscle is a paired muscle located on the lateral sides of the abdominal wall.
The abdominal internal oblique muscle, also called 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. Its fibres run perpendicular to the external oblique muscle, beginning in the thoracolumbar fascia of the lower back, the anterior third of the iliac crest (upper part of the hip bone), and the lateral half of the inguinal ligament. The internal oblique is thinner and smaller than the external oblique.
The external oblique has several functions. It pulls the chest downwards and compresses the abdominal cavity, increasing intra-abdominal pressure. It also performs ipsilateral (same-side) side-bending and contralateral (opposite-side) rotation: the right external oblique would side-bend to the right and rotate to the left, and vice versa. The internal oblique muscle functions similarly, except it rotates ipsilaterally. The external oblique also contributes to a variety of trunk movements, including walking and running, which cause movements in the torso. It helps to control the movement of the spine, pelvis, and rib cage during gait.
The internal and external obliques work together to allow the trunk to twist and turn. Together with the back muscles, the abdominal muscles make up the "core" muscles. They help protect the spine and keep the body stable and balanced. They also help with movement of the body between the ribcage and the pelvis, allowing the trunk to be in constant motion. This supports the spine and trunk during walking, sitting down, standing up, or twisting from side to side.
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Abdominal oblique muscle injuries
The abdominal external oblique muscle is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. The internal oblique muscle, on the other hand, lies below the external oblique muscle and just above the transverse abdominal muscle. The internal oblique is much thinner and smaller than the external oblique. Both sets of oblique muscles work together when a person twists or rotates their body.
In the case of a 21-year-old male Australian football player, an acute oblique abdominal wall tear was caused by rotating to the left while in a forward-flexed posture to handball the ball. The injury resulted in severe right-sided abdominal pain, and the player was assisted off the field. An initial off-field assessment was performed, and the player began a graduated rehabilitation program consisting of four phases. After 35 days, the player returned to full match play without re-injury.
Conservative treatment, including rehabilitation and conservative management, is usually enough to treat oblique muscle strains and tears. This may include isometric strengthening, light stretching, and learning the abdominal draw-in maneuver to regain control of deep core muscles. After a few weeks of conservative treatment, a full recovery can typically be expected.
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Abdominal oblique exercises
The abdominal external oblique muscle is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. The abdominal internal oblique muscle lies below the external oblique muscle and just above the transverse abdominal muscle. The obliques are responsible for movements like bending from side to side and rotating the torso from left to right. They also assist with spinal flexion and help stabilize and protect the spine.
Side Plank
The side plank is a great exercise to challenge the oblique muscles. Assume a high plank position with your shoulders in line with your wrists and your neck neutral. Place your feet together and lift your right hand off the ground, rotating into a side plank position and opening your torso. Keep your right arm extended and follow the movement with your arm. Pause, return to the high plank, and repeat on the other side.
Russian Twists
Russian twists are a compound exercise that works the obliques, along with the abdominal muscles and hips. Sit on a yoga mat with a wide stance, holding an ab wheel with both hands. Keep your head in a neutral position, looking at the ground in front of you. Squeeze your shoulder blades, abs, and glutes to create tension. Turn the pits of your elbows forward, round your back, and press into the floor to roll out. Keep your back rounded and avoid arching. Pause when fully extended, then return to the starting position.
Windshield Wiper
The windshield wiper exercise can be done using a barbell to work on power and explosiveness, as well as your obliques. Position yourself in front of a barbell and grab the end of it with both hands overlapping. Keep your arms extended and move the barbell to your right hip, twisting your torso to follow it. Slightly bend your knees, keep your arms straight, and rotate your torso to bring the barbell up and over to the left hip. Pivot your feet to make the movement smooth. Repeat, alternating sides, until you reach the desired number of reps.
Squat with a Twist
Take a wide stance with your toes pointed out. Sink into a squat position and lift your arms out to your sides, bending your elbows at a 90-degree angle. Staying in the squat position, bend to your side, bringing your right elbow toward your right knee. Return to the center and crunch to the left.
Bird Dog
Start on all fours with your hands in line with your shoulders and your knees in line with your hips. Inhale, brace your core, and reach your right arm and left leg straight out so they're both parallel to the ground. Ensure your lower back stays stable and your hips remain square to the ground. Exhale and return to the starting position. Repeat with the left arm and right leg.
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Frequently asked questions
Abdominal oblique muscles are a pair of muscles located on the sides of the rectus abdominis. They are divided into two types: external oblique muscles and internal oblique muscles.
External oblique muscles are the outermost abdominal muscles, extending from the lower half of the ribs around and down to the pelvis. They cover the sides of the abdominal area and are large and sit on the top surface of the abdomen.
Internal oblique muscles 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 oblique muscles.
The external oblique muscles have various functions depending on whether they contract unilaterally or bilaterally. When contracting unilaterally, they rotate the trunk to the opposite side. When contracting bilaterally, they work with the internal abdominal oblique and rectus abdominis to flex the trunk anteriorly.
The internal oblique muscles work with the external oblique muscles to allow the trunk to twist and turn.
