Study of Postural Variation, Muscle Activity and Preferences of Monitor Placement in VDT Work

Various studies investigated sitting posture while working at VDT for muscle response, posture and preference, to deduce recommendations for design. The posture assumption is a dynamic activity and is often resulted out of continuous visual and physical feedback processed on cognitive level to maintain optimum comfort. The parameters that affect the work station design such as visual display terminal height directly affect the posture and comfort. This paper discusses the study of postural angles such as Head inclination, Trunk bending, Trunk inclination and sEMG muscle activity of Neck Extensors, Erector Spinae, Sternocleidomastoid and Upper Trapezius muscles when a Visual Display Terminal (VDT) user is working at a visual display terminal. The conditions were simulated on a test-rig which was developed on the basis of anthropometric data obtained. The experiment was performed on eight Indian male subjects and the VDT height was varied from 69.5 to 119.5 cm, monitor inclination was varied as 0, 30, 60°. Changes in the sitting postural angles was recorded using photogrammetry, simultaneously sEMG muscle activity of the defined muscles was recorded, also the preferred position of the VDT at each height as responded by the subjects was recorded including preferred VDT height. It was observed that the thoracic bending varied between 120 and 155° which increased with increasing VDT height. The trunk inclination with reference to horizontal varied from 96 to 65°. Similarly neck inclination was observed to change by a span of approximately 40°. The preferred monitor height was observed to be in the range of 89.5–99.5 cm. The Upper Trapezius and Sternocleidomastoid showed variation in muscle activity but not related to monitor height. The Erector Spinae and Neck extensors however responded to the variation in monitor height in exactly opposite pattern. It was observed that the point of intersection of the normalized sEMG ratio curves lies in the span of preferred VDT height responded by the subjects. The potential application of this research is in design of Sit down console, computer work stations/consoles with or without adjustability features in Indian context.