Monday, June 1, 2009

Motor control, Back pain & Transverse abdominis

Recently the focus has shifted to motor control than strength because “a strong muscle may lack a proper motor control over the joint it controls” (one may call it inability in strength). This might cause a array of dysfunction or painful disorders in a joint of it’s concern or may also be a cause for a disorder away from that place where the muscle does not exerts it’s works (Because of long kinetic chains i.e. effects of weakness in any part of the chain has a repercussion on other parts of the kinetic chain).

Many research articles off late on back pain focusing on muscle dysfunction in patients with low back pain have led to discoveries of impairments in deep muscles of the trunk and back. The muscle impairments are not those of strength but rather problems in motor control (1).

When it was found that it is not strength that has to be augmented rather a motor control has to be reinstituted; the approach of physiotherapy has also changed to “a motor learning exercise protocol” (1).

Hence to start rolling a rehabilitation protocol under such circumstances, the initial focus is on retraining the co-contraction of the deep muscles i.e. the transversus abdominis and lumbar multi-fidus (1).

In this review we will only discuss about transverse abdominis with both acute and chronic low back pain in terms of reducing the neuromuscular impairment and in control of pain.

Contribution of transverse abdominis:
There has been considerable interest in the literature regarding the function of transversus abdominis, the deepest of the abdominal muscles, and the clinical approach to training this muscle (3).

Anatomy of Transverse abdominis Muscle: this muscle spans dorso-ventrally. It originates on the internal surfaces of the 7th-12th costal cartilages, thoracolumbar fascia, iliac crest, and lateral third of the inguinal ligament, and it inserts (finishes) on the linea alba with the aponeurosis of the internal oblique, pubic crest, and pectin pubis via the conjoint tendon.

Exploring the kinetic chain connecting Shoulder & transverse abdominis:
For execution of shoulder functions require a stable spine. Research indicates that contribution from Tr. Abdominis is a key to stability of the spine during execution of functions involving shoulder.

Hodges & colleagues tried to explore
1. Chronological sequence of trunk muscle activity associated with arm movement &
2. To determine if dysfunction of this parameter (vide point no1) was present in patients with low back pain.

They found:
1. Movement in each direction resulted in contraction of trunk muscles before or shortly after the deltoid in control subjects.
2. The transversus abdominis was invariably the first muscle active and was not influenced by movement direction, supporting the hypothesized role of this muscle in spinal stiffness generation.
3. Contraction of transversus abdominis was significantly delayed in patients with low back pain with all movements.

This study by Hodges & colleagues also found an important thing i.e. there is a delayed onset of contraction of transversus abdominis indicates a deficit of motor control and is hypothesized to result in inefficient muscular stabilization of the spine further resulting in LBA syndromes.

The SI joint & transverse abdominis:
Epidemiological reviews of LBA have recently revealed that nearly 30% of all cases of LBA are due to SI joint dysfunction. Richardson & colleagues studied, role of transverse abdominis in relation to LBA due to sacroiliac joint laxity. They found:

1. The independent contraction of the transversus abdominis significantly decreases the laxity of the sacroiliac joint.
2. This decrease in laxity is larger than that caused by a bracing action using all the lateral abdominal muscles.
These findings are in line with the authors' biomechanical model predictions and support the use of independent transversus abdominis contractions for the treatment of low back pain.

Changes in postural control of transversus abdominis in LBA: Comparison of EMG of spinal muscles.
In another study involving EMG of Hodges & colleagues transversus abdominis, rectus abdominis, erector spinae, and oblique abdominal muscles found, the EMG onset of transversus abdominis was delayed in the LBP subjects with movement in each direction, while the EMG onsets of rectus abdominis, erector spinae, and oblique abdominal muscles were delayed with specific movement directions. The result of this study provides evidence of a change in the postural control of the trunk in people with LBP.

Does posture training help patients with LBA?
We have already discussed that Tr.Abdominis is intimately associated with lumboscaral stability & lack of which causes LBA from SI or lumbar region. We have also discussed that training of Tr.Abdominis leads to manage pain and dysfunction in this area. However postural advice forms a key component of physio’s advice in management of LBA. Then the next question is does posture training have impact on Tr. Abdominis?

To date, there have not been any investigations into the influence of lumbo-pelvic neutral posture on TrA activity. Reeve & colleagues studied whether posture influences TrA thickness which ultimately answers role of transversus abdominis (TrA) on spinal stability may be important in low back pain (LBP).

20 healthy adults were recruited and taught five postures:
(1) Supine lying;
(2) Erect sitting (lumbo-pelvic neutral);
(3) Slouched sitting;
(4) Erect standing (lumbo-pelvic neutral);
(5) Sway-back standing.

In each position, TrA thickness was measured (as an indirect measure of muscle activity) using ultrasound. Then a comparison was done in the thickness of Tr.Abdominis which shows the impact of posture on Tr.Abdominis. The findings are as follows:

1. Erect standing > sway-back standing
2. Erect sitting > slouched sitting

This study concluded, lumbo-pelvic neutral postures may have a positive influence on spinal stability compared to equivalent poor postures (slouched sitting and sway-back standing) through the recruitment of TrA. Therefore, posture may be important for rehabilitation in patients with LBP & spending time in training good posture is a worthwhile investment.

Reference (s):

1. Jull GA et al; J Manipulative Physiol Ther. 2000 Feb;23(2):115-7.
2. Hodges PW et al; Spine. 1996 Nov 15;21(22):2640-50.

3. Hodges PW; Man Ther. 1999 May;4(2):74-86.

4. Richardson CA et al; Spine. 2002 Feb 15;27(4):399-405.

5. Hodges PW et al; J Spinal Disord. 1998 Feb;11(1):46-56.
6. Reeve AMan Ther. 2009 May 12. [Epub ahead of print]

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