The muscles of abdomen are flat, broad, and strong, holding up the internal viscera in place. They can be distinguished and separated according to their topographical location. Thus, they can be grouped into the anterior, lateral, and posterior abdominal wall muscles. Action: when they contract, they move the trunk in different directions in relation to the pelvis: forwards, sideways, and backwards. Exercising them help reduce the unhealthy white fat located around the waist.
The muscles of the anterior abdominal wall are: 1) the rectus abdominis muscle, which is the most conspicuous and the longest of them all, popularly known as the washboard when a person has an athletic figure; 2) the pyramidalis muscle, which is small and triangular, lying at the base of the rectus abdominis.
The muscles of the lateral abdominal wall are: 1) the external oblique muscle, which stretches obliquely from the ribs all the way down to the anterior half of iliac crest (of pelvis); 2) the internal oblique muscle, which lies under the external oblique, arising from iliac crest and inguinal ligament to be inserted into tenth to twelfth ribs; 3) transversus abdominis muscle, which is flat and broad, occupying the deepest layer of the anterolateral aspect of the abdominal wall.
The muscles of the posterior abdominal wall are: 1) the quadratus lumborum muscle, which is the only one on this side of abdomen. It is a paired flat muscle, which fills the space between the twelfth rib and the posterior portion of iliac crest of pelvis, being separated from the deep muscles of back by the deep layer of the lumbar fascia. It is innervated by intercostal and lumbar nerves (from T12 to L3).
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| Muscles of abdomen; anterior and lateral aspect. The external oblique muscle is cut away as it covers the internal oblique. |
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| Above, the external and internal oblique muscle. |