title: Effect of visual display terminal height on the trapezius muscle hardness: quantitative evaluation by a newly developed muscle hardness meter.
abstract: The aim of this study was to determine trapezius muscle hardness in 9 healthy volunteers before and after word processing tasks with a video display terminal (VDT) at three different heights. When using a desktop personal computer (PC), no change was observed in muscle hardness even after a 30-min task if a subject was in the reference posture with a declination angle formed by the Reid's line directed toward the upper edge of the PC screen and the horizontal plane within 5-10 degrees. However, an increase in muscle hardness was observed after a 15-min task in a posture of looking up at the screen (angle of elevation: 15-20 degrees) and after a 30-min task in a posture of looking down at the screen (angle of declination: 15-20 degrees). When the same 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.
authors.affiliation: Department of Bio-Medical Engineering, Tokai University School of High-Technology for Human Welfare, Shizuoka, Japan. horikawa@wing.ncc.u-tokai.ac.jp
authors.forename: M
authors.initials: M
authors.lastname: Horikawa
mesh_terms: D000328:Adult; D016288:Computer Terminals; D004867:Equipment Design / Q000295:instrumentation; D006804:Ergonomics / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009140:Musculoskeletal Diseases / Q000209:etiology / Q000517:prevention & control*; D009784:Occupational Diseases / Q000209:etiology / Q000517:prevention & control*; D014584:User-Computer Interface