Influence of sitting postures on neck and shoulder e.m.g. during arm-hand work movements

The aim of the study was to analyze the effect of different sitting postures on the level of activity in some neck and shoulder muscles in a standardized work cycle involving movement of the arm/hand. Ten experienced female workers volunteered in a laboratory study. Full-wave rectified, low-pass filtered, time-averaged and normalized e.m.g. was used. Surface electrodes were applied unilaterally at six locations. The course of the level of muscle activity during the standardized work cycle is presented. There was a tendency to higher level of activity when the arm/hand was moving along the high part of the work object compared to along the low part. The level of activity during the standardized work movement with the arm/hand was significantly influenced by the sitting postures chosen. The highest activity levels were found in the posture with the whole spine flexed. A marked reduction of the level of activity was obtained when a posture with the thoraco-lumbar spine slightly inclined backward was used.