title: Keyboard reaction force and finger flexor electromyograms during computer keyboard work.
abstract: This study examines the relationship between forearm EMGs and keyboard reaction forces in 10 people during keyboard tasks performed at a comfortable speed. A linear fit of EMG force data for each person and finger was calculated during static fingertip loading. An average r2 of .71 was observed for forces below 50% of the maximal voluntary contraction (MVC). These regressions were used to characterize EMG data in force units during the typing task. Averaged peak reaction forces measured 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 and 5.4 times the key switch make force (0.47 N). Individual peak or mean finger forces obtained from EMG were greater (1.2 to 3.2 times) than force measurements; hence the range of r2 for EMG force was .10 to .46. A closer correspondence between EMG and peak force was obtained using EMG averaged across all fingers. For 5 of the participants the force computed from EMG was within +/-20% of the reaction force. For the other 5 participants forces were overestimated. For 9 participants the difference between EMG estimated force and the reaction force was less than 13% MVC. It is suggested that the difference between EMG and finger force partly results from the amount of muscle load not captured by the measured applied force.
authors.affiliation: Center for Ergonomics, University of Michigan, Ann Arbor 48109-2117, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Martin
authors.forename: T J
authors.initials: TJ
authors.lastname: Armstrong
authors.forename: J A
authors.initials: JA
authors.lastname: Foulke
authors.forename: S
authors.initials: S
authors.lastname: Natarajan
authors.forename: E
authors.initials: E
authors.lastname: Klinenberg
authors.forename: E
authors.initials: E
authors.lastname: Serina
authors.forename: D
authors.initials: D
authors.lastname: Rempel
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003201:Computers; D004576:Electromyography; D006804:Ergonomics; D005260:Female; D005385:Fingers / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*