The external oblique is a pair of large, thin, superficial muscles that lie on the lateral sides of the abdominal region of the body. Contraction of certain muscles may result in several different actions, but they are best acknowledged for their lateral flexion and rotation of the trunk known as a side bend. The external obliques get their name from their location in the abdomen external to the internal abdominal obliques and from the direction of their fibers, which run obliquely (diagonally) across the sides of the stomach.
The external abdominal obliques have their origins with the lateral ribs 5 through 12 and insert into the linea Alba of the abdomen, the pubis, and the iliac crest of the hip bones. Their shape is approximately rectangular, with the long axis running anterior to posterior along the lineaAlba. Muscle fibers in the external obliques run medially and inferiority from the origins to the insertions across the lateral sides of the abdomen and end lateral to the rectus abdominis muscles.
The location and structure of the external abdominal obliques give them many different possible actions. Contraction of both external obliques results in the abdomen (as in sucking in the gut) or the flexion of the trunk (as in performing a crunch or sit-up). Contraction of one of the abdominal obliques results in the lateral flexion and rotation of the nose on the opposite side; in other words, the left external oblique rotates and flexes the trunk to the right.
External Oblique Functions
The external oblique muscle does the following:
Laterally Flexes the Spine
This means that the external oblique muscle bends the spine to the side (i.e., it moves the ribcage down to the bottom towards the pelvis).
Rotates the Spine
This means that the external oblique muscle turns the spine to the side (i.e., it twists the torso).
Compresses the Abdominal Cavity
This means that the external oblique muscle constricts the abdominal cavity organs and can increase intra-abdominal pressure (i.e., during a Valsalva maneuver).
Other Functions of the External Obliques
- Pulling the chest down to compress the abdomen
- Supporting the abdominal wall
- Assisting with forced expiration in breathing
- Bending from side to side
It originates from the external cover of the lower eight ribs 5-12.
The most posterior fibers are directed vertically and other fibersanteromedially. The internal obliques insert onto the costal cartilages of the lower 4 ribs, the abdominal aponeurosis (a superficial sheet of connective tissue over the abdomen), and the linea alba.
The upper two-thirds of the external abdominal oblique is supplied by lower intercostal nerves T7-T11 and subcostal nerve T12. The lower third provided by the iliohypogastricL1 from lumbar plexus.
Upper 2/3 receives blood supply from branches of lower posterior intercostal and subcostal arteries, smaller 1/3 from the deep circumflex iliac artery.
The external oblique muscle originates from the outer surface of the middle of the shaft of the lower six ribs as fleshy fibers. At its origin, the upper four slips and smaller four slips interdigitate with the serratus anterior and the latissimus dorsi muscles, respectively. The muscle gradually becomes aponeurotic, which inserts into the whole length of the linea alba extending onto the pubic crest and the pectineal line. Lower fleshy fibers attach to the outer lip of the anterior two-thirds of the iliac crest. Muscle fibers are directed obliquely downwards and medially.
The Muscle has Some Essential Features
- the inferior free border between the anterior superior iliac spine and the pubic tubercle is thickened and rolls inwards to form the inguinal ligament.
- The posterior fleshy open border forms the anterior boundary of the lumbar triangle (of Petit).
- The upper part of the aponeurotic layer crosses over the rectus abdominis muscle contributes to building the anterior segment of the rectus sheath.
- The lower part of the aponeurotic layer creates the middle half of the inguinal canal; medial attachment provides a V-shaped gap (superficial inguinal ring) to ensure passage of the spermatic cord/round ligament.
The weakness of EO muscle with other abdominal muscles increases the risk of hernia, umbilical hernia, for example.
Bilateral muscle weakness decreases the capacity of trunk flexion, and you can see anterior pelvic tilting from standing position in cases of bilateral weakness.
Trigger points: AO may form trigger points due to passionate strain, extra load during workouts, or even new activity, due to incision, direct trauma, or secondary due to different visceral pathology.