Does the posture kneeling chair reduce the risk of back pain?
In the lower back the lumber spine maintains a curvature known as the lumbar lordosis, which balances the compressive forces through the spine, between the lumbar discs and the facet joints.
In the sitting posture the lumbar spine straightens and consequently these compressive forces are disproportionately managed by the disc. For those who sit for long periods at a desk, it can be very difficult not to slump. This in turn can cause a reverse curve in the lumbar spine and therefore increase the stress through the discs even more, which can cause dehydration and fatigue of the disc, ultimately leading to degeneration and pain.
The disc is made up of a fibrous outer layer the annulus fibrosis and a gel nucleus. Increased force through the disc can lead to tearing of the annular fibres allowing the nucleus to prolapse posteriorly. The posterior outer fibres of the disc contain pain receptors that can be activated by continuous strain through the disc. The postural muscles of the lower back also contain pain receptors, which can become active as the these muscles fatigue under the strain of the compression to the spine If the outer fibres of the disc are breached, the nucleus will enter the spinal canal where the spinal cord is housed or reticular canal, where the nerve roots are housed. This can cause major irritation to the membranes covering these structures, causing severe back and leg pain, often referred to as sciatica.
The anatomy of the spine is not really designed to be in a seated posture for long periods. Ancient civilisations and indigenous populations of today, tend to squat, rather than sit. In the squat position the lower back adopts the lumbar lordosis of the standing posture and balances the compressive forces through the discs and facet joints reducing the risk of degenerative changes and pain.
It is important therefore for those that sit for long periods to use an ergonomic chair that promotes good posture. There is debate as to whether the kneeling posture chair is better suited to this role than the straight back chair. Studies are mixed on the superior benefits of the kneeling posture chair which is designed to share the strain of sitting through the shins and the buttocks, so as to reduce the compressive forces through the lumbar spine. One study found that the posture kneeling chair allowed the lumbar spine to adopt a curvature closer to that of standing posture, during sitting, typing and writing. It suggested that this may aid treatment of lower back injury. This design ensures the thighs are dropped to an angle of 60-70 degrees from vertical, whereas in a straight back chair the thighs are at 90 degrees. This modification in the angle of the thighs tilts the pelvis to promote the standing lumbar curvature.