Objective: The aim of this study was to investigate the effects of sustained computer keyboard typing on the human musculoskeletal system by assessing the pressure-pain threshold (PPT), scapular position and activation of the upper trapezius. Methods: Vertical and horizontal positional changes of the scapular were measured with a palpation meter before and after keyboard work, and the PPT was measured using a pressure algometer. Activation of the upper trapezius during 20 minutes of computer keyboard work was measured by electromyography, and four consecutive 5-minute segments were analyzed. Results: The vertical distance from the seventh cervical process to the acromion, and the horizontal distance from the inferior angle to the same level of the spinal process were significantly increased after keyboard typing work compared with before keyboard typing work ( p <0.05). The average value of the upper trapezius activity increased with increased time at the keyboard. The percent reference voluntary contraction of phase 1 (from start to 5 minutes) was lower than those of phase 2 (from 5 to 10 minutes), and phase 3 (from 10 to 15 minutes) ( p <0.05). Conclusions: We observed that sustained computer work changed the scapular position in the stretched upper trapezius. To prevent musculoskeletal problems in the shoulder region, posture reeducation during computer work should be considered in terms not only of neck and trunk posture, but also of scapular position.(J Occup Health 2013; 55: 167–172)