THE EFFECT OF KEYBOARD KEYSWITCH MAKE FORCE ON APPLIED FORCE AND FINGER FLEXOR MUSCLE-ACTIVITY

The design of the force-displacement characteristics or 'feel' of keyb oard keyswitches has been guided by preference and performance data; t here has been very little information on how switch 'feel' alters musc le activity or applied force. This is a laboratory-based repeated meas ures design experiment to evaluate the effect of computer keyboard key switch design on applied finger force and muscle activity during a typ ing task. Ten experienced typists typed on three keyboards which diffe red in keyswitch make force (0.34, 0.47 and 1.02 N) while applied fing ertip force and finger flexor electromyograms were recorded. The keybo ard testing order was randomized and subjects typed on each keyboard f or three trials, while data was collected for a minimum of 80 keystrok es per trial. No differences in applied fingertip force or finger flex or EMG were observed during typing on keyboards with switch make force of 0.34 or 0.47 N. However, applied fingertip force increased by appr oximately 40% (p<0.05) and EMG activity increased by approximately 20% (p<0.05) when the keyswitch make force was increased from 0.47 to 1.0 2 N. These results suggest that, in order to minimize the biomechanica l loads to forearm tendons and muscles of keyboard users, keyswitches with a make force of 0.47 N or less should be considered over switches with a make force of 1.02 N.