External Oblique: Definition, Function & Aponeurosis

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  • 0:04 External Oblique Muscles
  • 0:54 Function
  • 1:36 Aponeurosis
  • 2:54 Lesson Summary
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Lesson Transcript
Instructor: Alexandra Unfried

Alexandra earned her master's degree in nursing education and is currently a hospital supervisor/administrator.

The external oblique is a muscle that is part of the abdominal muscles. This lesson will discuss what the external oblique muscles are, what they do, and what the aponeurosis is.

External Oblique Muscles

Phillip was outside raking leaves for several hours. The next day he notices tenderness and pain on the left side of his abdominal wall. His external oblique muscles are very sore.

There are four main muscle groups making up the abdominal muscles. They include the rectus abdominis, transverse abdominis, internal obliques, and external obliques. The external oblique muscles are located on the outer surface of the sides of the abdomen, on each side of the rectus abdominis. The muscles extend from the lower ribs to the pelvis. The external oblique muscles are responsible for the twisting of the trunk. However, the rotation of the trunk is opposite to the side of the external oblique that is contracting. In other words, the right external oblique is working when the body twists to the left.

Phillip is right handed, so he holds the rake to twist to the right side of his body. That is why his left external obliques are sore.


Besides twisting the trunk of the body, the external oblique muscles are also responsible for movement of the spine, including:

  • Pulling the spine forward as the external oblique contracts (like in crunches or sit-ups)
  • Stabilizing the core
  • Moving the spine in any direction

Other functions of the external obliques are:

  • Pulling the chest downward to compress the abdomen
  • Supporting the abdominal wall
  • Assisting with forced expiration in breathing
  • Bending from side to side

The entire act of raking leaves involved Phillip's external obliques. He had a constant twisting motion as he moved the rake back and forth to collect leaves. He was breathing heavily while working and using his external obliques with his breathing while stabilizing his core and supporting the abdominal wall.


An aponeurosis is a pearly white tissue made up of fibers that takes the place of tendons. It is flat and runs along a wide space. It attaches muscles to moving parts of the body, either other muscles or bones. The aponeurosis of the external oblique runs down the center of the abdomen, starting at the bottom of the ribs and ending at the pubis. It's part of the sheath of the rectus abdominis and runs crosswise to attach the obliques to the other abdominal muscles.

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