Do you spend the majority of your work day sitting at a desk? If your answer is yes, you may also be experiencing some discomfort and even back pain from sitting for an extended period. 
We know that sitting too long creates pressure on the spine, distorting spinal curves and compressing discs. All of this can cause pinching of the nerves in the spinal cord, leading to numbness, tingling and serious back pain.
While the spine can maintain a natural curvature without the lower back support provided by the seat-back, the natural tendency for most people when sitting for an extended period is to slouch forward.
This slouching posture pushes the lower back out so that the natural inward curve goes in the opposite direction – outward toward the chair – straining the structures in the lower back. It is essential that the back be flush because this is what provides the support for the lower back.
Overall, the lumbar back support should keep the spine in a very natural position. It should not overly accentuate the inward curve, nor should it feel unsupported.