Co-contraction and the Transversus Abdominus in Low Back Pain

    One of the common findings in individuals with low back pain is poor utilization of the core musculature. The TA (transversus abdominus) has been found to be highly suspect in these cases. Any activity that involves movement of the extremities, first requires some sort of weight shift (it may be small) to assure stability. This is usually accounted for by a contraction of the TA right before the movement of the extremity. Studies have found that individuals with low back pain have delayed recruitment and decreased motor firing of the TA in activities.

    A common therapy technique in individuals with low back pain is to provide neuromuscular education on how to first fire the TA (and other core muscles) and then utilize them during daily activities. The theory is that since the TA encircles the abdomen/core (when combined with the internal obliques) and connects to the thoracolumbar fascia. When the TA contracts, it stiffens the fascia and creates a stabilized cylinder that is the core! There have been many exercises developed with the focus on isolating and educating usage of the TA, such as pelvic tilts. This study looked at the potential for using co-contraction to increase the motor control of the TA. The researchers found increased activity and thickness of the TA when resisted ankle dorsiflexion was combined with the abdominal draw-in maneuver. While the results are very interesting, there are many things that should be considered when examining this study. First of all, the study had a low sample of participants at 40 individuals that were conveniently selected. The measuring of TA baselines and improvements were questionable as well. Surface EMGs were used to measure activity and can receive interference relatively easily from other muscles due to their proximity. Ultrasound imaging was used to measure the thickness of the TA and other abdominal musculature. The methods to this study were questionable, but the results provided interesting findings that could potentially be incorporated in future studies and interventions.

                                                                    Anatomy Review ("Kendall"):

Transversus Abdominus (TA):
Origin: inner surfaces of cartilages of the lower 6 ribs, interdigitating with the diaphragm; thoracolumbar fascia; anterior 3/4 of internal lip of the iliac crest; and lateral 1/3 of the inguinal ligament.

Insertion: linea alba by means of a broad aponeurosis, pubic crest, and pecten pubis.

Innervation: T7-12, L1 iliohypogastric and ilioinguinal, ventral divisions.

Action: acts like a girdle to flatten the abdominal wall and compress the abdominal viscera; upper portion helps to decrease the infrasternal angle of the ribs, as in expiration. This muscle has no action in lateral trunk flexion, except that it acts to compress the viscera and to stabilize the linea alba, permitting better action by the anterolateral trunk muscles.

References:
Chon SC, You JH, Saliba SA. "Cocontraction of ankle dorsiflexors and transversus abdominis function in patients with low back pain." J Athl Train. 2012;47(4):379-89. Web. 09/28/2012.

Kendall F, McCreary E, Provance P, Rodgers M, Romani W. "Muscles: Testing and Function with Posture and Pain." 5th ed. Baltimore: Lippincott Williams & Wilkins, 2005. 197. Print.