A POSTURAL MODEL FOR THE REDUCTION OF NECK TENSION (VDT, ELECTROMYOGRAPHY, WORKSTATION, ERGONOMICS)

It was the purpose of this study to produce a mathematical model for the prediction of neck muscle tension based on source document placement at a word processing workstation. Such a model should reflect tension present in both static and dynamic situations. For this reason both reading and typing tasks were examined. A mathematical model would allow source document effects to be modified through work station design modifications.;In addition to EMG data, film was taken to establish angles of head flexion, lateral flexion, and rotation. Head position was compared to both source document placement and level of muscular tension.;ANOVAs performed for neck tension by document position indicated significant differences in tension measures with changes in both horizontal and vertical displacement angles of the source document. The highest levels of muscle tension and the greatest head flexion and rotation angles were found in the two placements which had documents flat on the table to the side of the keyboard.;The lowest values for all parameters were produced in the two central document positions. Levels of tension differed significantly between typing and reading tasks only in the extreme document positions.;Subjects for this study were 20 adult volunteers with varying degrees of typing skills. Each subject was asked to perform a reading task and a typing task in each of six source document positions. During task performance the levels of muscular tension in the neck extensor muscles and in the sternocleidomastoid muscles was sampled using electromyographic techniques. These tension levels were then compared to the subject's resting level of tension for control and then transformed into a percentage of the maximum level of tension produced in a voluntary isometric contraction.;To produce the mathematical model tension in each of the muscle groups was regressed on horizontal and vertical document angles. The regressions for both extensor groups were found to be significant in both the reading and typing conditions. The model was further enlarged to include equations in which head position was regressed on measures of document position. The complete model consists of eight equations, four for typing and four for reading.;From this study it was concluded that source document positioning plays a significant role in the production of tension in the neck extensor muscles. This tension may be a result of head position, with head position related directly to document position.