Effects of the wrist angle on the performance and perceived discomfort in a long lasting handwriting task

Since wrist joint position affects the length of finger muscles and then on the grip force, its influence on handwriting product quality and efficiency was studied in this research. We performed a repeated measures experiment to test whether the angle of wrist extension has a significant influence on the kinematic characteristics, handwriting production and the perceived soreness of writing hand. Forty young adults (aged 18 to 22) performed a continuous writing task (30 minutes) on a computerized system which measured the wrist joint angle and documented the handwriting process. The tasks were performed on a 2-D digitizing tablet. The top panel of the tablet records the position when the pen comes in contact with its surface or within 1 cm of its surface. An electrogoniometer was used for recording the wrist extension angle during the writing tasks. According to the progression of self perceived soreness, subjects were classified into “effortless” and "hard” groups. The wrist joint angle and in-air trajectory length (i.e., the length of non-writing while writing) were found significant different between the two groups in the writing process. “Hard” group was consistently associated with longer in-air trajectory length, as well as with more extended wrist joint. Instead, the other characteristics such as writing speed, in-air time, on-paper time, and pentip pressure were not found significant different between the two groups. The wrist extension angle was significantly correlated with the perceived soreness as well as with the ratio of in-air to on-paper time. The results of this study indicate that ergonomic and biomechanic analysis provides important information about the handwriting process. Less extended wrist may result in more effort needed in the work activity of handwriting such that more soreness perceived by the subjects.