Effects of keyswitch stiffness, typing pace, and auditory feedback on typing force, muscle activity, and subjective discomfort.

Abstract

Typing force has been identified as a possible risk factor for the development of work related musculo-skeletal disorders. A series of five studies were conducted to examine the effects of keyswitch stiffness, typing pace, and auditory feedback on typing force, muscle activity, and subjective discomfort. A summary of the major findings appears below. For rubber dome keyboards increasing make force causes typing force and EMG to increase. The ratio of typing force to make force decreases as make force increases and can be modeled as: Typing force/Make force = 3.833 $\sp*$Make Force$\sp{\wedge(-0.681)}$ for rubber dome keyboards. This model agrees with empirical data from other studies on rubber dome keyboards with an r$\sp2$ = 0.67. The design of the keyswitch may have more of an effect on typing force than keyswitch stiffness. Subjects typed with comparable force levels on a 0.72 N buckling spring keyboard and a 0.28 N rubber dome keyboard. These results suggest that the feedback characteristics of the keyboard may be more important than the keyswitch stiffness. Relative typing pace is more important than actual typing speed in determining muscle activity and discomfort. Subjects that type faster can do so without requiring more muscle activity. However, if the fastest subjects are required to type at a faster pace (e.g. as fast as they can) there will be an increase in muscle activity and discomfort. The ratio of typing force to make force can be modeled as: Typing force/Make force = 3.833 $\sp*$Make Force$\sp{\wedge(-0.681)}$ * Pacing Factor with the following pacing factors: Slow (50%) = 0.84, Normal (82%) = 1.0, and Fast (93%) = 1.1. This model agrees with empirical data from other studies on rubber dome keyboards with an r$\sp2$ = 0.95 Enhanced auditory feedback can be used to reduce typing force and EMG 15-20% and has an almost immediate effect. After one week of periodic feedback subjects type with less force and EMG during the day regardless of presence or absence of feedback.