Internal Oblique Muscle: Action, Origin & Insertion

Instructor: Dan Washmuth

Dan has taught college Nutrition, Anatomy, Physiology, and Sports Nutrition courses and has a master's degree in Dietetics & Nutrition.

The internal oblique is very important muscle when celebrating your birthday. Find out why, as well as the action and origin of this muscle, by reading the rest of this lesson.

Happy Birthday!

One of the best parts of a birthday is getting to blow out the candles on a birthday cake. Think about the last time you did this, you probably took a big breath in and then blew the air out of your mouth very forcefully in order to blow out all of the flames. Did you know that your internal oblique muscle helped you do this?

The internal oblique muscle is a muscle that is found at each side of the body, just lateral to the abdomen. The word 'oblique' means 'diagonal' or 'slanted', which is a reference to the slanted direction that the muscle fibers of this muscle run up the sides of the body.

The internal oblique is a diagonal muscle located at each side of the body.
internal oblique

Origin of the Internal Oblique

The internal oblique originates from three different locations, which are described by the following chart.

Point of Origin Description
Iliac crest The top, outer rim of the pubic bone.
Inguinal ligament The diagonal band of connected tissue at the front of the pubic bone.
Thoracolumbar fascia The membrane of connective tissue located at the back of the thoracic and abdominal cavities.

The inguinal ligament (shown in green) is one of the points of origin of the internal oblique muscle.
inguinal ligament

Insertion of the Internal Oblique

The internal oblique inserts onto the costal cartilages of the eighth through twelfth ribs and the linea alba. Costal cartilage is the section of cartilage that extends from front ends of the ribs, and the linea alba (Latin for 'white line') is a band of connective tissue that runs up the middle of the abdomen.

Action of the Internal Oblique

There are several different actions of the internal oblique muscles, which are described in the following chart.

Action of the Internal Oblique Description
Flexion of the trunk Bending the trunk forward, such as when you bend over to pick something up off the ground.
Lateral rotation of the trunk Turning the trunk to either side, such as when you turn around to look at someone behind you.
Lateral flexion of the trunk Bending the trunk to either side, such as when you perform side bends

Additionally, the internal oblique assists with forced exhalation, such as when you blow out birthday candles. When the internal oblique contracts, it helps push the air out of the lungs, helping to create a more powerful and forceful exhale.

The internal oblique muscles assist with forced exhalation, such as when a person blows out birthday candles.
blowing

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