The external oblique is visible at low body fat percentages. The muscle appears as a series of diagonal lines connecting to the six-pack.
The external oblique originates from the 5th – 8th ribs, and insert at several points (linea alba, iliac spine, pubic crest, and the iliac crest).
The functions of the external oblique are to aid in rotation (chopping down a tree), flexion (bending over), and lateral flexion of the spine (bending to the side).
The internal oblique sits between the transverse abdominis and the external oblique. The origin is from the iliac crest, and the lower part of the pelvis. The insertion is at the linea alba, pubic crest, and the lower 3-4 ribs.
The internal oblique serves the exact same functions as the external oblique - aiding rotation, flexion and lateral flexion of the spine.