The lumbar tissues are undoubtedly injured more often than those of the extremities in performing an upper extremity task. The spinal mechanismbecomes a pertinent example of the interaction between muscle, on one hand, and ligament, bone, and joint on the other. In the normal lumbar spine there exists a lordotic curve or anterior curve. This curve serves to support the axial compression that gravity and bipedal stance put upon the spine. Often increased ipilateral muscle hypertonicity and extreme repetitive compressive forces will transfer that load onto the facet joints of the corresponding vertebrae. This causes aberrant motion, increased shearing stress, chronic muscular tension, capsular ligamentous sprain, pain, and premature degeneration of the facet joints.

When using the BackSystem3 the lumbar lordosis is decreased, which opens the facet joints. Maximum lumbar spine flexion pulls the posterior ligament system tight and produces a parallel vertebral end-plate. The posterior annulus is pulled tight, as is the ligamentum flavum. This increases the A to P or mid-sagittal diameter of the canal.

IN COMPARISON, maximum lumbar spine extension approximates the bodies, posteriorly causing the annulus to collapse. The lamina also approximates the bodies posteriorly, causing the annulus to collapse. The lamina,also approximate, causing the ligamentum flavum to buckle, anteriorly. This diminishes the A to P or mid-sagittal diameter of the spinal canal. While moving from the seated position, the weight of the user's upper body is shifted forward, over the thighs. This shifting maneuver creates a non-compressive force, resulting in a gravity stretch of the lumbar vertebrae, facets, and related soft tissue structures.