Testing TvA Function

Question:

With the exercise Abdominal Draw Leg Slide, you can use the blood pressure cuff as a bio-feedback. I have always read that you would pump the cuff to 40mmhg and then you activate the TvA by drawing in the belly button towards the spine. Then you would increase the pressure by 20-30mmhg. When you are standing, you wouldn't flatten your back whenever the TvA is activated. I have never had it fully explained why it is necessary to increase the pressure. So my question is why?

Answer:

There are two major stabilizer systems of the body, the inner unit and the outer unit. The inner unit is composed of the transversus abdominis (TvA), some fibers of the obliquus internus, the musculature of the pelvic floor, the multifidus and the diaphragm. The TvA is the key muscle of the inner unit system.

The TvA, in concert with other inner unit muscles, activates to increase stiffness of spinal joints and the sacroiliac joints. Activation of the inner unit provides the necessary “stiffness” to give the arms and legs a working foundation from which to operate. The inner unit is part of a system of stabilizer mechanisms, all of which are dependent on the integrated function of all inner unit muscles.

It is simple to test your TvA for proper function. To test yourself, lie face down and place the bladder of a blood pressure cuff (BPC) directly under the umbilicus. Pump the BPC to any even number between 40-70 mmHg (after exhalation), completely relax, exhale and draw your umbilicus off the BPC. Have someone watch carefully to make sure you are not pressing downward with your arms, flexing your hips or using your gluteus maximus muscles (keep the glutes relaxed). If your TvA function is normal, you should be able to reduce the pressure in the BP cuff by 10 mmHg without any movement of your spine, without flexing your hips or pressing your shoulders into the floor.

In addition to testing yourself for proper activation of the TvA, you can also test your lower abdominal coordination by testing your ability to control sacral base inclination (pelvic tilt). Inability to control sacral base inclination can cause instability of the sacroiliac joints and is also considered a contributing factor to such spinal pathology as spondylolistheses, spondylolysis, spinal instability and disc herniation.

To test yourself, lie on your back and place your hands under your spine (palms down). When your fingertips are just behind your umbilicus (L3), flex your hips to 90 degrees and keep your knees fully relaxed. Perform a slight posterior tilt. The backward motion of your pelvis (posterior pelvic tilt) should place slight pressure on your hands. Now, while holding the pressure on your fingers with your spine, begin lowering your feet to the floor, always keeping the knees fully relaxed. If you have normal lower abdominal coordination, you should be able to slowly lower your feet to the floor and bring your legs back to the point of 90 degree hip flexion without the pressure of your lower back ever coming off your fingers.

With knowledge of these two assessments, let’s now take a look at the Abdominal Draw Leg Slide. This exercise can help to increase strength AND coordination of the lower abdominals. The GOAL is to perform the exercise without preferentially recruiting the hip flexors (which will be noted by an increase in lordosis or inward curvature of the lower back). This exercise can be beneficial to those clients who display poor coordination between the lower abs and the hip flexors, which is displayed by early recruitment of the hip flexors made visible by loss of neutral spine into an anterior tilt. To successfully complete this exercise, you need to be able to maintain the slight posterior pelvic tilt position that we just learned is a measure of lower abdominal coordination.

It is maintenance of the posterior pelvic tilt that is responsible for the pressure on the BPC, and the ability to keep that pressure constant while extending the leg is a measure of the ability to maintain pelvic/abdominal stabilization. So it is not a flattening of the back that puts pressure in the BPC when the TvA is activated in this exercise but instead maintenance of the slight posterior pelvic tilt used to maintain a neutral spine (or prevention of anterior tilt).