Effect of visual display terminal height on the trapezius muscle hardness:quantitative evaluation by a newly developed muscle hardness meter

The aim of this study was to determine trapezius muscle hardness in 9 healt hy volunteers before and after word processing tasks with a video display t erminal (VDT) at three different heights. When using a desktop personal com puter (PC), no change was observed in muscle hardness even after a 30-min t ask if a subject was in the reference posture with a declination angle form ed by the Reid's line directed toward the upper edge of the PC screen and t he horizontal plane within 5 IV However, an increase in muscle hardness was observed after a 15-min task in a posture of looking up at the screen (ang le of elevation: 15-20 degrees) and after a 30-min task in a posture of loo king down at the screen (angle of declination: 15-20 degrees). When the sam e tasks were performed with a notebook PC, muscle hardness increased after 15 min. Fifteen minutes of relaxation exercise reduced the muscle hardness caused by VDT work. (C) 2001 Elsevier Science Ltd. All rights reserved.