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Biomechanical loading on the upper extremity increases from single key tapping to directional tapping.

Qin J; Trudeau M; Katz JN; Buchholz B; Dennerlein JT
J Electromyogr Kinesiol 2011 Aug; 21(4):587-594
Musculoskeletal disorders associated with computer use span the joints of the upper extremity. Computing typically involves tapping in multiple directions. Thus, we sought to describe the loading on the finger, wrist, elbow and shoulder joints in terms of kinematic and kinetic difference across single key switch tapping to directional tapping on multiple keys. An experiment with repeated measures design was conducted. Six subjects tapped with their right index finger on a stand-alone number keypad placed horizontally in three conditions: (1) on single key switch (the number key 5); (2) left and right on number key 4 and 6; (3) top and bottom on number key 8 and 2. A force-torque transducer underneath the keypad measured the fingertip force. An active-marker infrared motion analysis system measured the kinematics of the fingertip, hand, forearm, upper arm and torso. Joint moments for the metacarpophalangeal, wrist, elbow, and shoulder joints were estimated using inverse dynamics. Tapping in the top-bottom orientation introduced the largest biomechanical loading on the upper extremity especially for the proximal joint, followed by tapping in the left-right orientation, and the lowest loading was observed during single key switch tapping. Directional tapping on average increased the fingertip force, joint excursion, and peak-to-peak joint torque by 45%, 190% and 55%, respectively. Identifying the biomechanical loading patterns associated with these fundamental movements of keying improves the understanding of the risks of upper extremity musculoskeletal disorders for computer keyboard users.
Biomechanics; Computer-equipment; Equipment-operators; Ergonomics; Force; Keyboard-operators; Motor-control; Musculoskeletal-system; Musculoskeletal-system-disorders; Physiological-response; Posture; Statistical-analysis; Work-analysis; Work-performance; Work-practices; Author Keywords: Tapping; Upper extremity; Kinematics; Kinetics; Biomechanical loading
Jack T. Dennerlein, Harvard School of Public Health, Department of Environmental Health, 401 Park Drive, Room 404L, Boston, MA 02115
Publication Date
Document Type
Journal Article
Email Address
Funding Type
Fiscal Year
Identifying No.
Grant-Number-R01-OH-008373; Grant-Number-T42-OH-008416; B11232011
Issue of Publication
Priority Area
Services; Wholesale and Retail Trade
Source Name
Journal of Electromyography and Kinesiology
Performing Organization
Harvard University School of Public Health
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division