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Computer keyswitch force-displacement characteristics affect muscle activity patterns during index finger tapping.

Authors
Lee-DL; Kuo-PL; Jindrich-DL; Dennerlein-JT
Source
J Electromyogr Kinesiol 2009 Oct; 19(5):810-820
NIOSHTIC No.
20036077
Abstract
This study examined the effect of computer keyboard keyswitch design on muscle activity patterns during finger tapping. In a repeated-measures laboratory experiment, six participants tapped with their index fingers on five isolated keyswitch designs with varying force-displacement characteristics that provided pairwise comparisons for the design factors of (1) activation force (0.31 N vs. 0.59 N; 0.55 N vs. 0.93 N), (2) key travel (2.5mm vs. 3.5mm), and (3) shape of the force-displacement curve as realized through buckling-spring vs. rubber-dome switch designs. A load cell underneath the keyswitch measured vertical fingertip forces, and intramuscular fine wire EMG electrodes measured muscle activity patterns of two intrinsic (first lumbricalis, first dorsal interossei) and three extrinsic (flexor digitorum superficialis, flexor digitorum profundus, and extensor digitorum communis) index finger muscles. The amplitude of muscle activity for the first dorsal interossei increased 25.9% with larger activation forces, but not for the extrinsic muscles. The amplitude of muscle activity for the first lumbricalis and the duration of muscle activities for the first dorsal interossei and both extrinsic flexor muscles decreased up to 40.4% with longer key travel. The amplitude of muscle activity in the first dorsal interossei increased 36.6% and the duration of muscle activity for all muscles, except flexor digitorum profundus, decreased up to 49.1% with the buckling-spring design relative to the rubber-dome design. These findings suggest that simply changing the force-displacement characteristics of a keyswitch changes the dynamic loading of the muscles, especially in the intrinsic muscles, during keyboard work.
Keywords
Computer-equipment; Computers Equipment-design; Equipment-operators; Ergonomics; Keyboard-operators; Musculoskeletal-system; Physiological-response; Posture; Statistical-analysis; Work-analysis; Work-performance; Work-practices; Author Keywords: Finger; Keyswitch; Force-displacement characteristics; Design; Keyboard; Computer; Electromyography; Force; Motor control
Contact
Jack T. Dennerlein, Department of Environmental Health, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115
CODEN
JEKIE3
Publication Date
20091001
Document Type
Journal Article
Funding Type
Grant
Fiscal Year
2010
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-008373; Grant-Number-T42-OH-008416
Issue of Publication
5
ISSN
1050-6411
Priority Area
Services
Source Name
Journal of Electromyography and Kinesiology
State
MA
Performing Organization
Harvard University School of Public Health
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