Adjustment of the seated workplace--with special reference to heights and inclinations of seat and table

Abstract

The influence of varying workplace adjustment on posture, muscular load, and subjective acceptability has been investigated in eight studies. Workplace variables were: seat height, seat inclination, backrest position, table height, and desk inclination. Moreover, some of the adjustments were investigated in relation to the tasks: desk-work, typing, large-scale drawing, and simulated assembly work. Concerning posture, the static aspect was investigated by statometry, while the dynamic aspect was estimated by analysing the movements transferred to a tiltable seat. Muscular load was assessed by means of amplitude distribution functions derived from electromyography. A five-point scale was used for subjective rating. It is recommended that the seat should be height adjusted approximately 3-5 cm above popliteal level, and the table top 3-5 cm above elbow level. A slanted desk, placed on a horizontal table, is recommended, as it had greater positive influence on the posture than varying seat adjustments. These recommendations are in accordance to subjective preferences, and to a compromise between optimizing the posture and using the backrest. In addition, the recommended seat adjustment seemed to induce more body movements than the traditionally recommended height just below popliteal level. With the high chair adjustment, the seat should be able to incline forward. A tiltable seat seemed preferable, but it is still a question whether or not such equipment facilitates movements. The backrest has been demonstrated to be a much lesser determinator for shifting the lumbar spine towards lordosis, than a slanting desk or an increased seat height. The backrest should be pushed against the back after the subject's selection of the position on the seat. This usually corresponds to an ischial-tuberosity position 6-7 cm behind the axis for seat-tilting. During touch-typing the keyboard should be at the level of the elbows, whereas the significance of a forearm/wrist support is unclear.