Influence of screen and copy holder positions on head posture, muscle activity and user judgment

A study was conducted on eight subjects, in order to investigate the influence of head posture with regards to the screen and copy holder position, the activity of cervical muscles and the subjective judgement given by the subjects. A total of eleven different positions (exercises) of screen and copy holder were investigated. Four different screen positions were examined in the upright (middle) sitting posture and three different screen positions were investigated in the backward sitting posture. In addition, four different positions of the copy holder were examined in the upright sitting posture. Head posture and muscle activity were continuously measured in each exercise for a duration of 5 min. At the end of each exercise, the subjects were asked how they judged the position of the screen and/or the copy holder in comparison with other positions. The results show that preference is to be given to a screen position in which the vision axis is horizontal or inclined slightly downwards . The copy holder should be arranged at one side of the screen