The following is courtesy of Richard Gamble, a structural integration practitioner in Fayetteville, NC.  An anatomy book might come in handy while you are reading this.

A common prescription for those who have chronic back pain is to strengthen their abdominal muscles to help “support” the lumbar spine by counterbalancing the erector spinae. The answer to why this method does or does not work lies in recognizing the different functions of two subsets of abdominal musculature, superficial and the deep.

The superficial abdominals consist of three layers laterally from superficial to deep:

• External obliques
• Internal obliques
• Transversus abdominus
• Rectus abdominus (anteriorly)

The two transversus abdominii wrap around the body between the ribs and iliac crests like a belt, increasing intra-abdominal pressure when they contract. The external oblique on one side of the body and the internal oblique on the other side contract to shorten the distance between the costal margin and iliac crest to which they attach, resulting in a rotation towards the internal oblique and an anterior shortening of the trunk. When both sets of obliques contract equally, the rotations cancel and there is a resulting anterior trunk shortening and an increase in intra-abdominal pressure. Contraction in the rectus abdominus results in trunk shortness anteriorly.

“The rectus is like a guy-rope that really has a large effect on all the structures above it, because it has such good leverage on the rib cage… The physics of the situation, in most cases, dictates that a hypertoned rectus will pull the ribs down toward the pubic bone, with a host of secondary results.”  Thomas Myers, Massage Therapy  May/June 1998 pg 54

The deep abdominals consist of the psoas and quadratus lumborum. The iliacus attaches on the lesser trochanter and the iliac fossa, directly affects pelvic tilt (creating lumbar hyperextension), but does not directly support the lumbar vertabrae. The quadratus lumborum strongly affects lateral tilt using the lever of 12th rib when contracting unilaterally; bilateral contraction of this muscle tends to draw the lower ribs closer to the iliac crest, compressing the lumbar spine, and limiting breathing by preventing the inferior edge of the ribcage from lifting during inhalation. The psoas originates on theT12-L5 vertebral bodies, discs, and transverse processes (TPs) and shares a tendinous attachment with the iliacus on the greater trochanter. The psoas’ route is not a direct one; this deep hip flexor passes anterior to the pubic bone along the way, giving it a much greater mechanical advantage than the erectors. Most anatomy texts do not show the psoas from a lateral view, when this phenomenon is visible, and its effect on tilts and rotations most apparent.

“The psoas creates hyperextension (lordosis) with its lower fibers and lumbar flexion (flattening of the lower back) with its upper fibers. The erectors and transversospinalis create lordosis and finally lumbar compression if they contract too hard.” Thomas Myers, Massage Therapy, July/August 1998 Pg 113

In summary, there are two muscles of the trunk that directly support the lumbar spine by counteracting forward flexion and lumbar hyperextension. They are the upper fibers of the psoas, and the transversus abdominii. The upper (outer) fibers of the psoas counteract hyperextension by flexing the upper lumbar spine. The transversus abdominii counteract flexion by increasing intra-abdominal pressure, lifting the thoracic spine through the costal attachments of the respiratory diaphragm. All of the other abdominals create shortness in the anterior trunk, placing more stress on the erectors. Both length and strength is required in all of the abdominals to support a healthy, flexible lumbar spine.

So, what does this mean?  All those sit-ups don't help.  They actually harm you.  Get the abs & psoas relationship in balance with Structural Integration.  Then general daily exercise will maintain the length and health of this area and without doing crunches or sit-ups.

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