The Transverse Abdominis: Its Role in Stabilization of the Back

We use the term “Core Stabilization” when we think of controlling our trunk by contracting our abdominals and back muscles and allowing movement of the limbs while keeping the trunk stable; thus having limbs moving on a stable base. Most people believe that if they perform crunches they will develop strong core muscles.

In the last ten years, research has shown that the main dynamic stabilizer of the lower back and pelvis is the transverse abdominis (TrA), the deepest of the abdominal muscles. Its muscular fibers run transversely, therefore, it is named according to its fiber orientation.

The transverse abdominis muscle attaches to the thoracolumbar fascia and the deep erector back muscles between the pelvic bone and rib cage posteriorly and from the lower six rib cartilages, linea alba (central facial structure) and the inguinal ligament anteriorly. It extends the entire length of the anterior trunk. Since it is the only abdominal muscle to attach to the posterior spine, it is considered the “human corset” of the trunk.

The transverse abdominis muscle when it contracts causes a drawing in (hollowing) of the abdominal wall. {Insert picture of person pulling in stomach}. At the same time it tightens the back muscles and fascia, thus reducing the shear and stress on the back. Research has found that when you initiate movement by lifting your arm or leg, the first muscle that contracts to stabilize your back is the TrA. Since most people are weak in the TrA muscle, then more forces are taken on the spine and cause increase stress and wear and tear on the vertebral spine.

To assist in helping someone to localize the activation of the transverse abdominis, a pressure biofeedback unit was developed to help keep the lumbar spine stable while contracting the transverse abdominis.

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Researchers in Holland found that several muscle groups working together help to stabilize the lumbar spine and pelvis. This is referred to as muscle slings. Maintaining local segmental control through initial drawing in of the abdominal wall to form the “corset” action is required prior to all exercise movements,

Since the transverse abdominis is poorly developed in most people, learning to activate this muscle without reverting to previous poor patterns of muscle control requires concentration. For example, if someone weak in core strength has to lift a heavy object, they will hold their breath to try to stabilize the trunk. When trying to learn to localize the TrA, most patients will try to substitute using the stronger rectus abdominis (six packs), holding their breath, or arching the back to try to use the back extensors.

The principle is to try to progress while keeping the lumbar spine in neutral without moving and not substituting with the other muscles mentioned above. There is pressure biofeedback device that helps to see if a person is keeping the transverse abdominis (TrA) hollowed in while trying to strengthen using the legs as resistance. The pressure biofeedback unit has an air-filled three-section bladder that is placed under the lumbar spine with the person positioned supine with the knees bent. The person begins with drawing the abdomen in to activate the TrA, keeping the back still while trying to breathe. The pressure sensor is inflated to 40 mmHg. The person watches the pressure dial and attempts to lift one leg after the TrA and back are maximally contracted, keeping the pressure steady during the lift at 40 mmHg.

The progression for trying to improve in control of the TrA while lifting the legs is as follows:

Forced expiration while trying to feel for the TrA muscle will help a person feel for the correct muscle activation.
Placing the person in all fours position, and pull the transverse abdominis inward without moving the back.
Placing the person prone with the bladder under the lower abdomen and then have the person draw the TrA inward. As the person draws in the stomach off the pad, the pressure in the pad is reduced. The pressure reduction is proportional to the degree to which the patient can elevate the abdominal wall. The pressure dial will be inflated to 70 mmHg and the dial will drop (usually at least 4-5mmHg) as the person draws the TrA inward.
Lifting one leg at a time, and alternating the legs lifted.
Bringing the hip flexors beyond 90 degrees and trying to lift the other leg after the one leg is already lifted.
Lifting one leg to 90 degrees of hip flexion, and while holding that position, then lift the other leg.
Lift one leg with the opposite arm overhead while supine and then lifting the other leg.
Lifting both legs together with no motion occurring in the lumbar spine.
Lifting both legs to 90 degrees of hip flexion, extending the knees then lifting both legs toward the ceiling without the back moving or rectus abdominis moving the abdomen wall outward.

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