Effect of different seat heights on lumbar spine flexion during stand-to-sit motion.
Wakana Shirouchi, Shinichiro Ishii, Sumiko Yamamoto
PMID 35035071WHAT IT FOUND
Standing up from a low seat requires much more forward bending of the lower back than standing from a standard seat.
The back flexes more because the pelvis tilts backward while the chest keeps tilting forward, increasing the mechanical load on the lumbar spine.
Key findings
01The maximum angle of lumbar spine flexion was significantly larger when participants sat from a lower seat compared to a standard seat.
02The increased lower back bending on the lower seat occurred because the pelvis tilted posteriorly while the thorax continued to tilt anteriorly, creating a larger timing difference between these movements.
03The study measured joint angles in healthy participants to infer lumbar load; it did not measure actual spinal forces or include patients with low back pain.
STILL TO COME
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What it does not show
The study included only healthy adults, not patients with low back pain, so the movement patterns may differ in the target population. The study measured kinematics (joint angles) but did not measure actual lumbar spine loads, muscle activity, or intradiscal pressure; increased flexion was inferred to increase load based on previous literature. The sample size was small (n=20). The study used a specific definition of 'lower seat' (60% of knee height), which may not reflect all clinical scenarios.
Declared interests
The authors declare no conflicts of interest.
The easy way to misread this
Do not assume that sitting on a low seat causes pain or injury in patients with low back pain. This study only showed that healthy people bend their backs more when sitting from a low chair; it did not test people with back pain or measure actual spinal forces.