abdominal internal oblique muscle

The abdominal internal oblique muscle (abdominal internal oblique) is one of the three flat muscles of the lateral abdominal wall. It lies deep to the external oblique and superficial to the transversus abdominis, forming the middle layer of the lateral abdominal wall.

The internal oblique is located on the lateral and anterior abdominal wall, between the external oblique on the outside and the transversus abdominis on the inside. Its fibers run obliquely upward and medially from the iliac crest and inguinal ligament to the lower ribs and the linea alba.

The internal oblique flexes and rotates the trunk, compresses the abdominal contents, and assists with forced expiration. When acting with the contralateral external oblique, it produces ipsilateral rotation of the trunk.

The internal oblique can be strained during sports involving twisting or rapid directional changes. It is also relevant in hernia repair surgery, as the internal oblique forms part of the inguinal canal's posterior wall and its integrity influences hernia recurrence rates.

The external oblique lies superficially and its fibers run downward and medially, while the internal oblique is deep to it with fibers running roughly perpendicular. Together, their opposing fiber directions create a strong, tension-resistant wall around the abdomen.