Lumbar spine curvature during office chair sitting

Prolonged sitting is generally accepted as a high risk factor in low back p ain and it is frequently suggested that a lordotic posture of the lumbar sp ine should be maintained during sitting. We asked whether the sagittal curv ature of the lumbar spine during sitting is affected by the seat tilt, back rest and the direction of the synchronised mechanism of the back and seat t ilt (synchro tilt). Two office chairs were tested by multibody analysis int erfacing a human model with a chair model. Results indicate that a synchron ised mechanism of an office chair representing a posterior tilt of the seat while the backrest is reclined maintains an evenly distributed lumbar lord osis. The segmental angles are between 3.1 and 3.6 degrees at the lumbar ve rtebrae 1/2-4/5 (L1/2-L4/5). These lumbar spine segmental angles are not se nsitive to the backrest height. In contrast, a synchro tilt concept with a reduction of the seat's posterior tilt while the backrest is reclined cause s a strong reduction of the lumbar lordosis in backrest recline with a maxi mum reduction from 11.7 to 2.8 degrees in L4/5. As a consequence of these r esults, a synchro tilt concept with a posterior tilt of the seat while the backrest is reclined is preferable from the lumbar spine kinematics point o f view. (C) 2001 IPEM. Published by Elsevier Science Ltd, All rights reserv ed.