Influences of Sitting Posture and Interface Activity on Human Physical and Psychological Reaction

The purpose of this study was to examine the influences of sitting posture and interface activity on some human physical and psychological parameters, such as lumbar surface Electromyography (sEMG) activities of erector spinae muscles (ES) and multifidus muscles (MF), body pressure distribution of human-chair interfaces and sitting discomfort, so as to provide a scientific basis on dynamic chair design and optimization and human-table-chair office system design. Ten healthy male subjects sat on two office chairs (one fixed dual-back chair with inactive interface and one motive dual-back chair with active interface) under three sitting postures (90°, 110° and 130° of seatpan and backrest angle). Six tests were performed on each subject and sEMG activities of left and right ES and MF and body pressure distribution data of seatpan and backrest were statically measured. Meanwhile the Body Part Discomfort (BPD) Scale (Revised) was used to measure the psychological reaction to sitting discomfort. The results showed that sitting posture and interface activity did not affect significantly on lumbar myoelectric activities (P>;0.05), and that sitting posture affected significantly on six pressure variables in the eight (P<;0.01) but interface activity affected significantly only on average seatpan pressure (ASP) (P<;0.01), and that low back discomfort (LBD) at the sitting posture of 130° was much lower than that of 90° and 110° (P<;0.01), and that total discomfort (OD) had a large difference between fixed dual-back chair and motive dual-back chair and the latter gained a higher rating of comfort. This study not only proved the best sitting posture of 130° but systematically utilized the combination of subjective and objective experimental methods to confirm that motive dual-back chairs were significantly better than fixed dual-back chairs which showed the superiority of dynamic chairs.