KEYBOARD REACTION FORCE AND FINGER FLEXOR ELECTROMYOGRAMS DURING COMPUTER KEYBOARD WORK

This study examines the relationship between forearm EMGs and keyboard reaction forces in 10 people during keyboard tasks performed at a com fortable speed. A linear fit of EMG force data for each person and fin ger was calculated during static fingertip loading. An average r(2) of .71 was observed for forces below 50% of the maximal voluntary contra ction (MVC). These regressions were used to characterize EMG data in f orce units during the typing task. Averaged peak reaction forces measu red during typing ranged from 3.33 N (thumb) to 1.84 N (little finger) , with an overall average of 2.54 N, which represents about 10% MVC an d 5.4 times the key switch make force (0.47 N). Individual peak or mea n finger forces obtained from EMG were greater (1.2 to 3.2 times) than force measurements; hence the range of r(2) for EMG force was .10 to .46. A closer correspondence between EMG and peak force was obtained u sing EMG averaged across all fingers. For 5 of the participants the fo rce computed from EMG was within +/-20% of the reaction force. For the other 5 participants forces were overestimated. For 9 participants th e difference between EMG estimated force and the reaction force was le ss than 13% MVC. It is suggested that the difference between EMG and f inger force partly results from the amount of muscle load not captured by the measured applied force.