Today, there is much confusion regarding proper use of the abdominal wall, especially during resistance training or heavy lifting activities. Currently, there are numerous organizations and elite coaches who instruct their students to push their abdominals out while passing through the sticking point of a lift. This is encouraged both with, and without the use of a weight belt.

The technique of pushing the abs out during a lift may be more founded in tradition than current anatomical knowledge. In this article, I will present an anatomically based explanation for proper abdominal wall function during resistance training and will use the squat to help demonstrate this.


Figure 1-A & 1-B

A deep diaphragmatic breath should be taken prior to initiation of the squat or any other heavy lift. This results in contraction and subsequent lowering of the diaphragm into the thoracic cavity which pushes the organs down and out onto the abdominal wall. As seen in Figure 1-A, inhalation causes the diaphragm to drop from its resting position (shown in blue) to a position representative of inhalation, which causes distention of the abdominal wall. This results in the umbilicus moving away from the spinal column.


After a full inhalation is achieved, the transversus abdominis (TVA) should be activated. Because the fibers of the TVA are horizontal with respect to the spine (Figure 2 – A1), when activated, it causes the umbilicus to move toward the spine. This inward movement is critical the following reasons:

  1. When the TVA is activated, the internal organs are compressed which creates intra-abdominal pressure (Figure 1-B). Although current research indicates that intra-abdominal pressure may not be as supportive as previously believed, TVA contraction creates what is referred to as hoop tension.


  2. The hoop tension created by the TVA drawing inward against the relatively non-compressible viscera creates a segmental stabilizing effect on the lumbar spine. As seen in Figure 2 (A1 & A2), the TVA pulls laterally on the thoracolumbar fascia (TLF)(1) and because the TLF attaches to both the spinous process and the transverse processes of each lumbar vertebra, activation of the TVA serves to stabilize each vertebra.


  3. The erector spinae musculature are housed in a fascial envelope which is stabilized when the umbilicus is drawn inward. When the erector spinae muscles contract within this relatively non-expansible envelope, pressure is exerted against the fascia, which produces an extension force on the forward bend or flexed spine. This is referred to as the Hydraulic Amplifier Mechanism (1,2). There is also speculation, that activation of the TVA in concert with the other stabilizer mechanisms mentioned here actually produces a slight extension effect on the spine, which has been called thoracolumbar fascia gain (1).


As you descend in the squat, the line of gravity relative to the load gradually moves forward which creates a progressively greater flexion moment on the lumbar spine. Something you may have experienced while squatting is that, as you progress toward the sticking point, there is greater load placed on your back. This requires a concomitant increase in stability to prevent unwanted compression, torsion and/or sheer of the spinal structures.



Figure 1-C

Up-regulation of the inner unit muscles (diaphragm, TVA, multifidus and pelvic floor) will be necessary to adequately stiffen the spinal column to protect the joint structures of the spine from injury. Based on extensive clinical observations, I propose that, when lifting at high intensities, the diaphragm (being a large, strong muscle) contracts with enough force to push the viscera downward. Because the viscera are relatively non-compressible, this will force the umbilicus outward (Figure 1-C).


Many anatomists and biomechanics consider the body to be a highly efficient and energy-conserving organism for reasons of survival during developmental times. The body’s tendency to conserve energy can been seen while performing a heavy lift, such as the squat. As described above, when the powerful diaphragm contracts to meet the progressive demand for stabilization of the spinal column and rib cage, the viscera will be forced downward and outward. This would demonstrate why many coaches and athletes have observed the abs pushing out during a lift.

As the abs are being pushed outward under the force of contraction from the superincumbent diaphragm, the TVA will be forced to work eccentrically. Most of you know that a muscle is approximately 30-40% stronger eccentrically than concentrically. This mechanism would not only allow the body to better stabilize the spinal column, it would do it at a reduced energy cost!


While initiating the squat, or during preparation for any heavy lift, the deep abdominal wall (inner unit) of a functional body will activate to provide segmental stabilization of the spine. This results in a visible inward motion of the umbilicus; the abs are going in. As you move through the sticking point, the relative load against the spinal column will be at a maximum and will therefore require a maximum contribution from both the inner and outer unit muscles. The inner unit muscles will act to stiffen the spinal column while the larger outer unit muscles will provide gross stability and motion.

To better appreciate this, one need only look at the line of gravity during the decent into a squat. The progressively larger lever arm against the spine will require an increasingly greater contraction of the erector spinae muscles to move the load in concert with the leg musculature. The massive contraction of the back muscles can not go unchecked by the large rectus abdominis and oblique muscles, or the spine would simply colapse into extension. Therefore we could say that there is co-contraction of the outer abdominal muscles against the back muscles to provide gross stability of the torso and move the load.

As this co-contraction takes place, there will be thickening of the rectus abdominis and oblique muscles, just as you would expect when contracting any skeletal muscle. Considering this along with the fact that the diaphragm can force the TVA into an eccentric contraction thus pushing the umbilicus away from the spine (while maintaining segmental stability), would make it appear to the observer or athlete looking in the mirror that the abs are moving out! However, what I have shown here is that in a properly functioning body, the inner unit musculature remains contracted (abs in) while the outer unit contracts to act as a gross stabilizer, pushing the abdominals progressively more outward as the load and need for gross stability increases.


What is critical, with regard to stability and longevity of the spine in anyone lifting heavy loads (or loads heavy enough to require natural interruption of the respiratory cycle) is the sequence of events. In the functional body, the umbilicus will move inward as an indicator that the segmental stabilizing mechanism is activated (3). As the demand for greater stiffness and stabilization of the torso increases, the diaphragm will force the TVA to contract eccentrically. In concert with this action there will be an increased activation of the rectus abdominis and oblique abdominal muscles, providing gross stability by the way of co-contraction against the spinal extensors. This will be recognized as the abs moving outward, during which time the inner unit muscles will continue to be active unless the lifter is wearing a lifting belt; belt wearing may completely alter the recruitment patterns of the core musculature.

For a much more comprehensive explanation of the core stabilizing mechanisms see my correspondence courses titled Scientific Back Training and Scientific Core Conditioning. For an in-depth review of the effects of weight belts on the back and back stability mechanisms, please see my article titled Back Strong and Beltless.


  1. Bogduk, N. Clinical Anatomy of the Lumbar Spine and Sacrum. (3rd. Ed.) New York: Churchill Livingstone, 1999.
  2. Gracovetsky, S., Farfan HF, Lamay C (1997). A mathematical model of the lumbar spine using an optimal system to control muscles and ligaments. Orthopedic Clinics of North America 8: 135-153.
  3. Chek, P. Scientific Core Conditioning. (correspondence course) Encinitas, CA: Chek Institute, 1993, 1999.