If you have lower back pain, you may have been advised to strengthen your abdominal muscles. Four muscles make up the abdominal wall: the rectus abdominis, the transverses abdominis and the internal and external obliques. Collectively, they help stabilize the lower back by increasing pressure within the abdomen. While some experts have advised specifically targeting the transversus to treat lower back pain, other researchers argue that contracting the entire abdominal wall results in greater spinal stability.
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Transversus Abdominis Activation
In a classic study published in 1996 in "Spine," Australian researchers asked healthy people and those with low back pain to raise one arm overhead, a task that requires spinal stabilization. The researchers found that in people with low back pain, there was a delay in the contraction of the transversus abdominis, compared to those without pain. The transversus is responsible for drawing in, or hollowing, the belly. While the authors of the study noted that it was unclear whether the delay in contraction of the transversus was related to the cause of back pain, many experts have since recommended exercises to strengthen the transversus to reduce the risk of low back pain.
Results of Transversus Strengthening
A study published in 2005 in "Physical Therapy" cast doubt on the value of targeted transversus abdominis exercise for low back pain. Fifty-five people with low back pain underwent an 8-week exercise program. Half performed a general workout program that included stretching and stationary bicycling. The other half practiced core strengthening exercises, focusing on the transversus, in addition to the general workout. Both groups improved on several measures of lower back pain. However, the general exercise group showed slightly greater short-term improvement than the core strengthening group.
Co-Contraction of Abdominal Muscles
More recent research has investigated the role of the other 3 abdominal muscles -- the rectus abdominis and internal and external obliques -- in stabilizing the spine. A study published in 2007 in the "Archives of Physical Medicine and Rehabilitation" found that activating all of the muscles of the abdominal wall in a "bracing" strategy while holding a weight in the hands created more spinal stability than targeting the transversus alone by hollowing the belly. The authors suggest that the transversus works together with the other abdominal muscles but is not more important in generating spinal stability.
Increasing Abdominal Pressure
The authors of the study in "Archives of Physical Medicine and Rehabilitation" note that activating the entire abdominal wall increases the pressure within the abdomen, which helps stabilize the spine. An article published in 2011 in "Clinical Biomechanics" lends support to that theory. The researchers conducted a study in which researchers modeled the forces on the lumbar spine. They found that contracting the entire abdominal wall raised abdominal pressure and stabilized the spine but that selectively engaging individual muscles did not contribute to greater stability.