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102 m a s s a g e & b o d y w o r k j a n u a r y / f e b r u a r y 2 0 2 0 addressing this tightness and helps increase mobility. Any treatment should start with general techniques that work to relax the region. After that, more specific treatments can be used to address a number of key muscles acting on the motion segment. Numerous muscles in the lumbar region have a primary role in maintaining stability and producing movement in the motion segments. Interestingly, the latissimus dorsi is not one of them, though it lies over the entire low-back region. This muscle lies over the other muscles that might be treated in conditions involving movement challenges with the motion segments. Yet, massage of the latissimus is valuable to create general relaxation before working on deeper layers. The next muscle layer we focus treatment on includes the three divisions of the erector spinae group: spinalis, iliocostalis, and longissimus. Clients often have pain in this muscle group, and massage can bring immediate improvement through pain reduction and increased mobility. These muscles are relatively superficial, so they are easy to address in treatment. Hypertonicity in the erector spinae group can produce significant reduction in range of motion and subsequent altered motion segment mechanics, so they are an important group to treat. These muscles seem to respond best to treatments that work in a parallel direction to their fibers running along the spine. Deep to the erector spinae are the multifidus and quadratus lumborum. The quadratus lumborum also impacts motion segment mechanics and plays a crucial role in spinal mobility, especially in lateral flexion movements. This muscle is best addressed by working lateral to the erector spinae group. Because it is farther away from the spine and not fully under the erector spinae muscles, it is a little easier to access Another condition involving the motion segments is intervertebral disk pathology, which is often the result of prolonged mechanical loading in the lumbar spine. Excess compression causes the nucleus to push out into the annulus and deform the disk. This disk deformation is the condition known as a disk herniation (Image 4). These degenerative changes also shift greater weight-bearing responsibility to the posterior part of the motion segment. They may also lead to pain or other degenerative changes in the spinal structures. The intervertebral disk is actually quite resistant to compressive loads. It can take long periods of compressive loading without deformation. Studies have attempted to identify how much compressive load lumbar disks can manage before causing an acute herniation or rupture. Under high compressive loads, the vertebral end plates will often fracture before causing a disk herniation. Another illustration of the importance of motion segment mechanics is lumbar fusion surgery. Surgeons perform a fusion when there is a severe degree of disk degeneration and additional movement within the segment risks further damaging spinal structures. The surgery limits or stops motion altogether at one segment. The intention is to decrease the cumulative forces that contribute to spinal dysfunction. Yet, decreasing motion at one segment also decreases motion at segments above and below the fused segment. The resulting limited mobility in the soft tissues that span the segment means they can no longer move through a full range of motion, which makes them more prone to chronic hypertonicity and contributes to back pain. Massage can help these soft tissues stay in a more healthy and functional state and reduce back pain. IMPLICATIONS FOR MASSAGE Normalizing muscular mechanics of the motion segment is a valuable goal of massage treatment. Hypertonic muscles that restrict ideal movement between adjacent motion segments are a root cause of back pain. Massage treatment excels at 3 Lumbar lordosis and the motion segment. With increased lordosis (blue line), weight-bearing shifts posteriorly (black arrow). Image from 3D4Medical's Complete Anatomy application. The facet joints of the spine are another region susceptible to altered motion segment mechanics. The facet joints have a minimal amount of loadbearing function in normal spinal mechanics. Yet, particular postural challenges, such as an exaggerated lumbar lordosis, shift the loadbearing vector to the posterior motion segment. When the weight shifts posteriorly, the facet joints must bear increased weight (Image 3). Carrying more weight makes the joints more susceptible to degenerative changes that may contribute to lumbar facet syndrome or arthritis. As noted earlier, the anterior structures of the motion segment are the primary ones bearing weight and transmitting compression loads through the spine. Long periods in poor posture combined with muscle tightness can increase compressive loads on the anterior motion segment components. Degenerative changes in the spine may result from these chronic compressive loads.