Kinematics of the wrist during a keying task: the effects of workstation design and work pace

Since the advent of keyboards into the workplace, workers began to experience disorders of the tendons and nerves of the upper extremities, referred to as cumulative trauma disorders, due to the repeated exertions and excessive movements. One of the major research voids in the study of occupational injuries to the wrist is the lack of understanding of the kinematic nature of the wrist during keying tasks. Changes in wrist position were measured on 9 males and 9 females while keying, in the flexion/extension and radial/ ulnar planes. This information was then used to determine the wrist dynamic characteristics, then wrist accelerations were derived. The effects of Gender, Keyboard Height (5 cm below sitting elbow height, at sitting elbow height, 5 cm above elbow height), Keyboard Angle (-30 degrees from horizontal, horizontal, +30 from horizontal), and Keying Rate( 110 and 90 percent of the individual's average typing rate) on wrist accelerations were scrutinized.

The results of this study indicated that, throughout the keying task, there were a significant changes in wrist position (p < 0.05). Keyboard Height was the only significant variable (p < 0.05) on the magnitude of mean peak wrist acceleration. The lowest magnitude of wrist acceleration occurred when the keyboard was positioned 5 cm below the user's sitting elbow height From these findings it appears that the methods used were effective in determining the kinematic nature of the wrist during a keying task. Specifically, the technique employed is adequate for measuring the accelerations of the wrist, but future research is needed to more accurately define the factors that influence the magnitude of wrist accelerations.