Research Finds Difference between Office Chair Angles on Postural Stress
A study on the impact of different office chair features on spinal posture while sitting found that seat pan tilt and some types of lumbar supports may offer negligible improvement in sitting postures, but overall, sitting for extended periods of time puts stress on the spine and may generate spinal injury. Perhaps something new needs to be invented to minimize end range postural stress and spinal compression over time.
What’s at Stake
Sitting involves flexing the hips and back and moves joints out of their neutral zones, which contributes to stress in the lower back. Even 20 minutes of spinal flexion can cause laxity in the ligaments and change the reflex action of spinal muscles. Over the years, office chair manufacturers have attempted improvements in their products that would lessen stress on the back and improve overall sitting postures, but standing postures that incorporate a neutral posture—where the lower back maintains its convex curvature and the pelvis keeps a slight forward tilt— remains the optimal stance for preventing back damage and pain.
Studies have found that chairs that help the sitter to extend their lumbar spine and anteriorly rotate their pelvis while sitting are the most helpful in reducing the likelihood of damage to the ligaments, muscles, and vertebrae. These types of chair features fall into three categories: thoracic supports, lumbar supports, and seat-pan tilting mechanisms. Of these three modifications, only one type of seat pan mechanism and lumbar supports have been radiographically studied. It is also unclear if men and women have similar lumbar lordosis and pelvic inclination.
This study examined lumbar spine and pelvic postures radiographically using three available seating features to determine which, if any of the three features caused an improvement in spinal or pelvic positioning during sitting. It also looked at posture responses in men and women to see if there were differences between them.
The study involved 28 participants (14 males and 14 females) with no recent history of lower back problems. The volunteers, whose mean age was 25 years, were not told about the conditions being tested or the relevant features of the products being tested. They were each radiographed in the standing and sitting postures using standardized postural and breathing instructions during their x-rays. Their radiographic measures were then compiled into the software program, and a statistical analysis was performed.
Researchers found that the lumbar postures of all participants were significantly flexed and extended in the seating position compared to the standing position. There was trivial improvement between those using postural interventions and the control groups whose chairs did not employ those features. There were slightly reduced levels of flexion with seat pan tilt features and lumbar support mechanisms, indicating potential value in these accommodations, but lumbar lordosis or intervertebral joint angles were not affected in any significant way across the improvement features. At the pelvic level, researchers found statistically significant results: The seat pan tilt configuration produced more anterior rotation of the pelvis and less flexion. The male subjects showed greater flexion during sitting than females.
Sitting places strain on the lower back, particularly at the L4/L5 and S5/S1 disc levels. Lumbar supports and some seat pan tilt features may be slightly helpful in reducing the stress put upon the lower back while in the seated position, but overall, there was minimal difference between the various office chair features on reducing lumbar lordosis or IVJ joint strain. What improvement was evident was local to the spinal segment, rather than posture as a whole. Male and female subjects displayed angle differences in the effects of sitting at the L1/L2 and L2/L3 IVJ joints and pelvis.
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