People commonly refer to the “upper” and “lower” abdominal muscles, but that’s not really an accurate description of the muscles that make up the abdominal wall. While an exercise may target either the upper or lower section, these muscles don’t work independently of each other, so they can’t be isolated in exercise. Understanding more about the construction of your abdominal wall may help you choose the best exercises to meet your fitness goals.
The Abdominal Wall Overview
The abdominal wall encases the abdominal cavity, which contains — and protects — most of the gastrointestinal organs. Its other function is to support your trunk and enable its movement. All in all, there are six different abdominal muscles: the transverses abdominis, the internal obliques, the external obliques and the rectus abdominis.
According to the American Council on Exercise, you can think of the abdominal wall as being arranged into three layers: superficial, intermediate and deep. The external and internal obliques, rectus abdominis (RA) and transverse abdominis (TVA) are all considered part of the deep layer. The muscles themselves are layered on top of each other like the individual layers of a sheet of plywood. These deep muscles work as a unit to control movement of the spine, rib cage and pelvis.
There are also three flat muscles: the external oblique, internal oblique and transversus abdominis. They are located on the sides of the abdominal wall and work to flex and rotate the trunk.
The rectus abdominis is where the proverbial “six-pack” of ab muscles resides. It’s a long, paired muscle that flanks the center line of the abdominal wall. Fibrous strips cross into the muscle at several points called the tendinous intersections. They’re what makes up the six-pack seen in people with low body fat.
In addition to assisting the flat muscles in tucking in your guts, the rectus abdominis enables flexing of the spine, allows the rib cage and pelvis to move toward each other and helps you bend sideways. It also springs into action when the you raise your head while lying on your back.
The external obliques are the largest and outermost flat muscle in the abdominal wall, located on each side of the rectus abdominis and attaching to the lower eight ribs. The lower and middle sections attach to the front crest of the pelvis and to the pubic bone.
Running almost at right angles to the external obliques are the internal oblique muscles. They form an inverted “V” shape and attached to the lower three ribs, the pelvis and the connective tissue of the lower back.
Both the external and internal obliques help to flex the rib cage and the pelvic bones together. They also help trunk to rotate and bend sideways. The external obliques are called “opposite side” rotators because the left oblique rotates the trunk to the right, and vice verse. The internal oblique muscles, however, rotate from the side they’re on.
This the deepest layer of abdominal muscles and plays an important role in exhaling air from the lungs, but isn’t involved directly in moving the trunk. However, interest in the muscle has grown with increasing evidence that it plays a crucial role in stabilizing the lumbar spine. It’s been shown to contract before the movement of a limb. People with lower back pain have delayed contraction of the transverses abdominus prior to activating their limbs. Strengthening this muscle helps protect you from injury and pain.