While the spine can maintain a natural curvature without lower back support provided by the seatback, the natural tendency for most people when sitting for a long 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.
When sitting in an office chair, a good lumbar back support should be flush against the small of the back. Many portable lumbar back supports are shaped specifically so that one end should be positioned up and the other down. When placed correctly, a lumbar back support should provide the following benefits:
It is important 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.
There are several types of lumbar back supports available in different types of office chairs:
Ergonomic chair. There are a number of ergonomic chairs that are ergonomically sculpted with a lumbar support curvature built into the chair. To test if the ergonomic chair fits well, the user should sit up straight, with the head, spine, and buttocks in alignment. Then sit all the way back against the seatback. The curve of the ergonomc chair should naturally follow the curve of the lower back.
Because this type of lumbar support is not adjustable, the ergonomic chair should be tested and examined prior to usage to ensure an appropriate fit.