Abdominal External Oblique Muscle

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Abdominal External Oblique Muscle

The abdominal external oblique muscle (also external oblique muscle, or exterior oblique) 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, its muscular portion occupying the side, its aponeurosis the anterior wall of the abdomen. In most humans (especially females), the oblique is not visible, due to subcutaneous fat deposits and the small size of the muscle.

It arises from eight fleshy digitations, each from the external surfaces and inferior borders of the fifth to twelfth ribs (lower eight ribs). These digitations are arranged in an oblique line which runs inferiorly and anteriorly, with the upper digitations being attached close to the cartilages of the corresponding ribs, the lowest to the apex of the cartilage of the last rib, the intermediate ones to the ribs at some distance from their cartilages.

Abdominal External Oblique Muscle
Abdominal External Oblique Muscle

The five superior serrations increase in size from above downward, and are received between corresponding processes of the serratus anterior muscle; the three lower ones diminish in size from above downward and receive between them corresponding processes from the latissimus dorsi. From these attachments, the fleshy fibers proceed in various directions. Its posterior fibers from the ribs to the iliac crest form a free posterior border.

Those from the lowest ribs pass nearly vertically downward, and are inserted into the anterior half of the outer lip of the iliac crest; the middle and upper fibers, directed downward (inferiorly) and forward (anteriorly), become aponeurotic at approximately the midclavicular line and forms the anterior layer of the rectus sheath. This aponeurosis formed from fibers from either side of the external oblique decussates at the linea alba.

The aponeurosis of the external oblique muscle forms the inguinal ligament. The muscle also contributes to the inguinal canal.

Just deep to the external oblique is the internal oblique muscle. These muscles are in the deepest layer of the abdominal wall.

External Oblique Muscle
External Oblique Muscle

Nerve supply

The external oblique muscle is supplied by ventral branches of the lower six thoracoabdominal nerves and the subcostal nerve on each side.

Blood supply

The cranial portion of the muscle is supplied by the lower intercostal arteries, whereas the caudal portion is supplied by a branch of either the deep circumflex iliac artery or the iliolumbar artery.

External Oblique Ridge

A smooth ridge on the buccal surface of the body of the mandible that extends from the anterior border of the ramus downward and forward with diminishing prominence. It marks the attachment of the buccinator muscle and its stability provides a reliable landmark for designing dentures or subperiosteal implants.

External Oblique Exercises

Strong oblique muscles translate to a better body in a number of ways. They support the spinal column, reduce the risk of type 2 diabetes (which is commonly linked to excess abdominal fat), and improve performance in physical activities involving quick movements and twisting.

Of course, they look great, too. The highly sought-after V-shape is often a byproduct of a healthy diet and toned obliques.

Say goodbye to standard crunches, and try these fat-burning exercises that target the oblique muscles.

Exercises to Tone Your Oblique Muscles
  1. Bicycle Crunch.
  2. Bicycle Crunch Part 2.
  3. Single-Leg Side Plank.
  4. Rotating Side Plank.
  5. Rotating Side Plank Part 2.
  6. Spiderman Push-Up.
  7. Cross-Body Mountain Climber.
  8. Russian Twist.

External Oblique Function

The external obliques on either side not only help rotate the trunk, but they perform a few other vital functions. These muscles help pull the chest, as a whole, downwards, which compresses the abdominal cavity. Although relatively minor in scope, the external oblique muscle also supports the rotation of the spine.
The internal abdominal oblique muscle is located closer to the skin than the transverse abdominal muscle. This muscle supports the abdominal wall, assists in forced respiration, aids in raising the pressure in the abdominal area, and rotates and turns the trunk with help from other muscles.

External Oblique Action

The external abdominal obliques are a pair of broad, thin, superficial muscles that lie on the lateral sides of the abdominal region of the body. Contraction of these muscles may result in several different actions, but they are best known for their lateral flexion and rotation of the trunk known as a side bend.

External Oblique Aponeurosis

The aponeurosis of the abdominal external oblique muscle is a thin but strong membranous structure, the fibers of which are directed downward and medially.

It is joined with that of the opposite muscle along the middle line, and covers the whole of the front of the abdomen; above, it is covered by and gives origin to the lower fibers of the pectoralis major; below, its fibers are closely aggregated together, and extend obliquely across from the anterior superior iliac spine to the pubic tubercle and the pectineal line to form the inguinal ligament.

In the middle line, it interlaces with the aponeurosis of the opposite muscle, forming the linea alba, which extends from the xiphoid process to the pubic symphysis.

That portion of the aponeurosis which extends between the anterior superior iliac spine and the pubic tubercle is a thick band, folded inward, and continuous below with the fascia lata; it is called the inguinal ligament.

The portion which is reflected from the inguinal ligament at the pubic tubercle is attached to the pectineal line and is called the lacunar ligament.

From the point of attachment of the latter to the pectineal line, a few fibers pass upward and medialward, behind the medial crus of the superficial inguinal ring, to the linea alba; they diverge as they ascend, and form a thin triangular fibrous band which is called the reflected inguinal ligament.

In the aponeurosis of the external oblique, immediately above the pubic crest, is a triangular opening, the superficial inguinal ring, formed by a separation of the fibers of the aponeurosis in this situation.