The Abdominals are composed of several muscles: the Rectus Abdominus, Transverse Abdominus, and the External and Internal Obliques.
The Abdominal muscles sit on the front and sides of the lower half of the torso, originating along the rib cage and attaching along the pelvis.
The Rectus Abdominus muscle is commonly known as the "six-pack" muscle of the abs. Thin bands of connective tissue give it that appearance.
The Transverse Abdominus (also known as the Transversus) is the deepest muscle of the core (meaning it's underneath all the other muscles). It wraps laterally around the abdominal area.
The fibers of External and Internal Obliques run diagonally on the body, allowing for angled movement.
Abdominal Muscle Functions
Flex the spine (bringing the rib cage closer to the pelvis). This is seen in the abdominal crunching movement. When the movement is reversed, the Rectus Abdominus acts to bring the pelvis closer to the rib cage (e.g. with a leg raise movement).
Acts as a natural weight belt, keeping your insides in. This muscle is essential for trunk stability as well as keeping your waist tight.
Internal and External Obliques
Work to rotate the torso and stabilize the abdomen.