The illustration shows the two exterior abdominal muscles. Visible are: The external oblique abdominal muscle, the rectus abdominis muscle, and the anterior serratus muscle (cranio-dorsal), which doesn't belong to the abdominal muscles. Covered are: The oblique internal abdominal muscle, the transverse abdominal muscle, and the pyramidalis muscle. The abdominal musculature has various functions, like e.g. inclining and rotating the torso, maintaining the upright posture of the body, and expiration. Athletes often have a so-called sixpack, due to hypertrophy of the rectus abdominis muscle as well as decrease of the subcutaneous fat tissue.