This month’s anatomy article is all about the abdominals. The abdominal muscle group is comprised of four layers; the rectus abdominus, external obliques, internal obliques, and transervsus abdominus (TA). The main roles of the abdominals are to move the torso; form a firm, flexible wall to protect the internal organs; assist in forceful expiration; and is involved in any action that increases intra-abdominal pressure such as coughing and vomiting.
The rectus abdominus or the six pack muscle is the most superficial of the abs. It is made up of two parallel muscles that are separated by the linea alba, which is a connective tissue that runs vertically from the bottom of the sternum to the pubic bone. At several places, the muscle is intersected by fibrous strips, known as tendinous intersections. The tendinous intersections and linea alba give rise to the six pack shape of the muscle.
The external oblique is the largest of the deeper muscles and its fibres run diagonally from the ribs down to the front of the pelvis and into the six pack. The internal oblique fibres run perpendicular to the external oblique. The obliques act to flex, side bend, and rotate the trunk. The external oblique on one side lines up with the fibers of the internal oblique on the other side. For example, twisting to the left is a result of the actions of the internal obliques on the left and the external obliques on the right.
The deepest layer of the abdominals is the TA. The TA acts like the body’s natural corset and attaches to the thoracolumbar fascia of the lower back and wraps around the body to the front. It works in conjunction with the pelvic floor muscle group to support and stabilise the individual segments in the lower back, and provide pelvic and thoracic stability.