FUNCTIONAL REHABILITATION Patrick Sexton, EdD, ATC, CSCS, Report Editor Specific Lumbar Stabilization Exercise: Theoretical Underpinnings

Jim F. Schilling MS, ATC, LAT, CSCS • Marian College

ACUTE AND CHRONIC low back pain affects believed to have lumbar segment instability. a large percentage of patients who seek medi- Clinicians should have a clear understanding cal care. Lumbar motion segment (vertebra- of the rationale for administering any treat- disc-vertebra) instability is a possible cause ment to patients who have low back pain. of low back pain. Anatomic structures that The purpose of this report is to review the may be compressed or stretched include neuromuscular and biomechanical rationale spinal nerve roots, ligaments, zygapoph- for specific exercise techniques that are yseal joint capsules, believed to facilitate dynamic stabilization annular fibers of the of lumbar spine motion segments. Key PointsPoints intervertebral disc, and 1 Maintenance of spine segment position vertebral end-plates. Spine Stability within the neutral zone is important for Clinical instability is normal function. defined as a decrease Spine stability is the result of passive con- in the capacity of the nective tissue restraints, active muscle con- Muscle contraction is essential for lumbar stabilizing system of traction, and neural control mechanisms.1 segment stability. the spine to maintain Passive restraints include the structure of the a motion segment vertebrae, zygapophyseal joints, interverte- Dynamic stabilization of the lumbar spine within its physiological bral discs, and ligaments. Neural control of can be enhanced through motor learning of limits, which can lead muscle activation patterns is mediated by specific muscle activation patterns. to structural changes, proprioceptive input to the spinal cord from neurological dysfunc- ligaments, tendons, and muscles. tion, and incapacitating pain.2 The motion Bergmark3 hypothesized that two dis- segment “neutral zone” is that portion of the tinctly different muscle systems maintain range of physiological intervertebral motion spine stability, which were designated as within which the spinal motion is produced global and local. The global muscle system with minimal internal resistance.2 Neutral consists of large muscles that provide general positioning of spine segments minimizes trunk stabilization against external loads, the overall internal stresses and the degree such as rectus abdominis, external oblique, of muscular effort required to maintain their and the thoracic portion of iliocostalis lum- normal alignment. Unfortunately, no valid borum. The local muscle system consists method for measuring the neutral zone has of tonically active muscles that are directly been established. attached to the individual vertebrae, which Lumbar stabilization exercise training includes the lumbar multifidus (LM), trans- is often implemented for patients who are versus abdominis, and posterior fibers of the

© 2008 Human Kinetics - ATT 13(4), pp. 34-36 34  July 2008 Athletic Therapy Today internal oblique muscles of the lumbar spine. The deep intersegmental muscles of the spine, such as the LM, are located close to the center of rotation for spine seg- ment movements, which contributes to maintenance of segment positioning within the neutral zone.

Lumbar Stabilization Mechanisms

Three mechanisms have been proposed as theoretical explanations for lumbar segment stabilization and specific stabilization exercise training techniques.4-6 The first theorized mechanism using mechanical models suggests that contraction of the deep abdomi- nal muscles (transversus abdominis and internal obliques) increases intra-abdominal pressure, which exerts hydrostatic forces on the pelvic floor and the diaphragm that creates a compressive stabilizing effect Figure 1 4 The thoracolumbar fascia of the lumbar spine showing on spine segments. Research findings again using posterior layer (PL), lateral raphe (LR), middle layer (ML), trans- mechanical models have since suggested that the intra- versees abdominus (TA), and internal oblique (IO), transverse process(TP), spinous process (SP) abdominal pressure created by the deep abdominal muscles provides a “stiffening” effect on the lumbar spine, rather than a compression force.5 (i.e., the union of the posterior and middle layers) to Tesh et al.5 evaluated two other lumbar segment merge with the aponeurosis of the deep abdominal stabilization mechanisms that had been proposed muscles. Tesh et al.5 argued that the arrangement of by previous researchers who had used mathematical the fibers of the TF suggests that the deep abdominal models.6 The first theoretical mechanism identified muscles primarily originate from the middle layer, tension of the thoracolumbar fascia (TF) as a factor which would not transmit significant tension through that contributes to lumbar segment stability. The TF the posterior layer. consists of three layers of fascia that encapsulate the A second mechanism that could create tension back extensor muscles. The anterior layer is comprised within the middle and posterior layer of the TF is con- of the fascia of the quadratus lumborum, which is traction of the erector spinae muscle group. Contrac- attached to the anterior surfaces of the transverse pro- tion increases the cross-sectional area of the muscle cesses of the lumbar vertebrae. The posterior layer of group, which could increase intracompartmental pres- the TF consists of multiple laminae that arise from the sure within the paraspinal space. A closed compart- deep abdominal muscles. The number of laminae is ment is formed by the middle and posterior layers of greatest in the distal portion of TF. The posterior layer the TF, the vertebral column, and the intertransverse inserts on the dorsal tips of the spinous processes, and interspinous ligaments. An increase in intracom- with the superficial fibers attached to the upper lumbar partmental pressure may generate “hoop tension” vertebrae, and the deeper fibers attached to the lower in the middle and posterior layers of the TF, which lumbar vertebrae (Figure 1). The stronger deep fibers could provide lumbar segment stability without deep of the TF posterior layer, combined with the greater abdominal muscle contraction.5 number of distal laminae, provide the lower lumbar The fiber arrangement in the posterior layer of the vertebrae segments with greatest mechanical support. TF has a “net-like” configuration. Lateral tension gen- The middle layer of the TF is attached to the lateral tips erated by the deep abdominal muscles may produce and the entire length of the transverse processes of the a caudocranial force that has the effect of “drawing lumbar vertebrae, which joins with the posterior layer together” the tips of the spinous processes.5 Similarly, in forming a sheath around the erector spinae muscle the orientation of the fibers of the middle layer of the group . From its insertion at the transverse process, the TF may generate lateral tension that draws the trans- middle layer of the TF passes through the lateral raphe verse processes together.5

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