Effect of asymmetrical buttock pressure on forces exerted in buttock movement when using a reclining chair.
Yasuyuki Nagata, Kenichi Kobara, Daisuke Fujita
PMID 34083878WHAT IT FOUND
The overall sliding force on the buttocks during reclining did not change with a 2 cm cushion height difference.
When pressure was asymmetrical, the high-pressure side had higher sliding force than the low-pressure side.
Key findings
01Total shear force normalized to body weight was similar in the symmetrical and asymmetrical seat conditions: 128.9 %BW versus 123.6 %BW (p=0.756).
02In the asymmetrical condition, left buttock shear force was 147.4 %BW and right buttock shear force was 105.6 %BW, with the left side higher (p=0.020).
03The 2 cm height difference produced higher left buttock pressure (154.5 mmHg) than right buttock pressure (127.0 mmHg, p=0.001); the 0 cm condition showed no significant left-right pressure difference (p=0.513).
STILL TO COME
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What it does not show
Sixteen healthy adult males were tested, so the results may not apply to older adults, people with disabilities, or wheelchair users. The study measured shear force and pressure, not pressure ulcers, comfort, pain, or long-term posture. The total shear force was not different between the symmetrical and asymmetrical seat conditions; the left-right difference was found only within the asymmetrical condition. The asymmetrical condition was created by a 2 cm cushion height difference with the left side always high, which may not match how asymmetry arises in real seating. The paper does not describe randomization, blinding, or order of the two seat conditions.
Declared interests
This study was supported by JSPS KAKENHI Grant Number 19K19896 for publication, and the authors declared no conflict of interest.
The easy way to misread this
Do not conclude that asymmetrical seating causes pressure ulcers or that a 2 cm cushion height difference is harmful in patients. The study measured forces in 16 healthy adult males, the total shear force was not different between conditions, and no pressure ulcers were assessed.