The abdominal muscles are composed of four groups of abdominal muscles:
- Straight abdominal muscle
(lat. rectus abdominis)
- External oblique abdominal muscle
(lat. obliquus externus abdominis)
- Internal oblique abdominal muscle
(lat. obliquus internus abdominis)
- Transverse abdominal muscle
(lat. transversus abdominis)
Straight Abdominal Muscle
(lat. rectus abdominis)
The straight abdominal muscles are the biggest abdominal muscles and above all, they are responsible for the six-pack look. Both of the longitudinal "strap-like" muscles of the straight abdominal muscles run from the breastbone to the pubic bone and are divided into 3 venters of the same size which are separated by tendinous intersections.
External Oblique Abdominal Muscle
(lat. obliquus externus abdominis)
The external oblique muscle runs along the outer side of the lower rib to the iliac crest.
Function: One-sided contraction causes the external oblique muscle to tilt the torso to the side.
Internal Oblique Abdominal Muscle
(lat. obliquus internus abdominis)
The internal oblique abdominal muscle is almost completely covered by the external oblique muscle and is considerably smaller.
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External Oblique Abdominal Muscle |
Internal Oblique Abdominal Muscle |

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Transverse Abdominal Muscle |
Straight Abdominal Muscle |

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Straight Abdominal Muscle |
Transverse Abdominal Muscle
(lat. transversus abdominis)
The transverse abdominal muscle forms the deepest layer of all the abdominal muscles. It is completely covered by the oblique abdominal muscles. The fibres of the transverse abdominal muscles run from the inner surface, the transverse processes of the lumbar vertebrae and the iliac crest to the tendon sheath of the straight abdominal muscle.
The transverse abdominal muscle and the oblique abdominal muscles form the waistline and contribute, along with the other abdominal muscles, to keeping the pelvis upright.
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