Abdominal muscles cover the anterior and lateral abdominal region and meet at the anterior midline. These muscles of the anterolateral abdominal wall can be divided into four groups: theexternal obliques, theinternal obliques, thetransversus abdominis, and therectus abdominis.
There are three flat skeletal muscles in the antero-lateral wall of the abdomen. The external oblique, closest to the surface, extend inferiorly and medially, in the direction of sliding one’s four fingers into pants pockets. Perpendicular to it is theintermediate internal oblique, extending superiorly and medially, the direction the thumbs usually go when the other fingers are in the pants pocket. The deep muscle, the transversus abdominis, is arranged transversely around the abdomen, similar to the front of a belt on a pair of pants. This arrangement of three bands of muscles in different orientations allows various movements and rotations of the trunk. The three layers of muscle also help to protect the internal abdominal organs in an area where there is no bone.
Thelinea alba is a white, fibrous band that is made of the bilateral rectus sheaths that join at the anterior midline of the body. These enclose therectus abdominis muscles (a pair of long, linear muscles, commonly called the “sit-up” muscles) that originate at thepubic crest andpubic symphysis, and extend the length of the body’s trunk. Each muscle is segmented by three transverse bands of collagen fibers called the tendinous intersections. This results in the look of “six-pack abs,” as each segment hypertrophies on individuals at the gym who do manysit-ups.
The posterior abdominal wall is formed by thelumbar vertebrae, parts of the ilia of the hip bones,psoas major andiliacus muscles, andquadratus lumborum muscle. This part of the core plays a key role in stabilizing the rest of the body and maintaining posture.
| Movement | Target | Target motion direction | Prime mover | Origin | Insertion |
|---|---|---|---|---|---|
| Twisting at waist; also bending to the side | Vertebral column | Supination; lateral flexion | External obliques; internal obliques | Ribs 5–12; ilium | Ribs 7–10; linea alba; ilium |
| Squeezing abdomen during forceful exhalations, defecation, urination, and childbirth | Abdominal cavity | Compression | Transversus abdominis | Ilium; ribs 5–10 | Sternum; linea alba; pubis |
| Sitting up | Vertebral column | Flexion | Rectus abdominis | Pubis | Sternum; ribs 5 and 7 |
| Bending to the side | Vertebral column | Lateral flexion | Quadratus lumborum | Ilium; ribs 5–10 | Rib 12; vertebrae L1–L4 |
This article incorporates text from afree content work. Licensed under CC BY 4.0. Text taken fromAnatomy and Physiology, J. Gordon Bettset al, Openstax.
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