Wrist and Shoulder Muscle Activity Changes across Computer Tasks

The computer workstation is a ubiquitous tool in the office work environment; however, its use varies across many different tasks from surfing the Internet to typing. The question, therefore, is how does exposure to different physical risk factors for musculoskeletal disorders vary across tasks? Fifteen adults (10 females, 5 males) completed tasks simulating work at a computer workstation. The tasks were typing text, completing an html-based form, editing a document, a graphics task, and finally navigating through a series of web pages. During these tasks the muscle activity of the wrist prime movers and three shoulder muscle groups were recorded using surface EMG. For the wrist, the extensors were the most active ranging on average from 8 to 25 percent of Maximum Voluntary Contraction amplitude, with the greatest activity occurring in the typing task. The wrist activity decreased when the work changed from a keyboard-based activity to predominantly mouse-based activity. For the shoulder, the greatest activity was in the Trapezius muscle. The shoulder muscles were most active when both the mouse and the keyboard were required by the task. In summary, wrist and shoulder muscle activities at a computer workstation depend upon the type of task at hand.