Locating the External Obliques
Description
There is an external oblique muscle on each side of the abdomen. Of the three broad muscles found on the sides of the waist, the external obliques are the most superficial. They are found just under the skin, and the internal oblique and transversus abdominis muscles lie beneath them.
The contractile (red) fibers of the external obliques wrap the sides of the waist as they descend from the ribs to the pelvis.
Insertion
At their upper ends, the external obliques attach primarily to the sides and front of the rib cage. At their lower ends, they attach to the iliac crest of the pelvis (where you would put your hands on your hips). They extend, by way of tendinous fibers, along the inguinal ligament of the groin.
At the front of the abdomen, the aponeuroses of the right and left external obliques meet at the linea alba.
How the External Obliques Act on the Skeleton
1 • Side Bending and Backward Pelvic Rotation
An external oblique can pull on the pelvis.
- It can pull the pelvis laterally toward the ribs (lateral inclination or side bending), and it can inhibit the movement of the pelvis in the opposite direction.
- It can rotate the pelvis backward, and it can inhibit its rotation in the opposite direction.
2 • Narrowing the Rib Cage
An external oblique can pull the thoracic ribs down toward the middle of the trunk, and it can inhibit their return to the starting position. The rib cage narrows in this movement. (Note that when we drop our rib cage like this, we tend to exhale.) If the rib cage doesn’t change its shape, the external oblique will cause it to turn to the front.
3 • Indirectly Mobilizing the Vertebrae
By pulling the pelvis or rib cage laterally (to the side), an external oblique can indirectly mobilize certain vertebrae, bending or rotating the spine at the waist, and inhibiting the spine’s movement in the opposite direction. It isn’t directly responsible for moving the spine, as it doesn’t attach to any of the vertebrae.
Situated obliquely on the sides of the trunk, the fibers of the external obliques mobilize the sides on which they contract.
How the External Obliques Act on the Viscera
The external obliques act in two specific regions of the belly.
1 • Compressing the Viscera below the Navel
The external obliques have a significant impact in the area of the lower belly, where their fibers are the longest: upon contraction, they press on the viscera principally below the navel, pushing them up toward the ribs. In addition, contraction of the external oblique on one side can push the viscera to the opposite side; it can move the viscera laterally.
2 • Supporting the Lower Abdomen
The external obliques have a specific action at their lower end: Their fibers stretch from the ninth and tenth ribs to the inguinal ligament, which is sometimes considered the tendon of the external oblique. When these fibers contract, the action pulls on the inguinal ligament and contributes to supporting the lower abdomen.
The external obliques can contract zone by zone. For example, they can contract at the level of the waist or at the level of the ribs. This means that we can pull in our belly in stages.
The external obliques can push the viscera up toward the thorax or out to the sides. They often act in conjunction with other abdominals.