Muscles regulate themselves during movement. Contraction and relaxation occur and change as the body moves and alters position. The multifidus, a deep muscle of the back is the focus of this study.
A real-time ultrasound test was done of the multifidus muscle in two groups of men. One group had a history of low back pain (LBP) for at least one year. The second (control) group did not have back pain. All men were laborers in Hong Kong.
Ultrasound images of the cross section (CS) of the multifidus muscle were compared for both groups in several positions. First the men were prone (face down). Then the size of the multifidus was measured while standing up and stooping forward. The CS was taken at 25 degrees and 45 degrees of forward stooping.
The authors report the CS increased in the control group when moving from prone to upright. This indicates the muscle was contracting during this time. CS decreased during the forward stoop postures. These changes may show that an increased force is needed to stabilize the low back when in the upright posture.
Men with LBP did not have the same CS changes with these same changes in posture. It appears that the multifidus muscle failed to respond in men with LBP. The muscle may not be able to generate the force needed to stabilize the spine. This was especially true when in the upright position.
More study is needed to find out what keeps the multifidus muscle from increasing in size (contracting). Without enough contraction, the muscle can't help stabilize the lumbar spine. Once this is sorted out, then a rehab program can be planned to help restore normal multifidus contraction in patients with LBP.
Sai-wing Lee, PhD, et al. Relationship Between Low Back Pain and Lumbar Multifidus Size at Different Postures. In Spine. September 1, 2006. Vol. 31. No. 19. Pp. 2258-2262.