Affiliations: Department of Environmental Health, Harvard School of
Public Health, Boston, MA, USA | Department of Environmental and Occupational Health
Sciences, University of Washington, Seattle, WA, USA | Department of Orthopaedic Surgery, Brigham and Women's
Hospital, Harvard Medical School, Boston, MA, USA
Note: [] Address for correspondence: Jack T. Dennerlein, Ph.D.,
Department of Environmental Health, Harvard School of Public Health, 665
Huntington Avenue, Boston, MA 02115, USA. Tel.: +1 617 384 8812; Fax: +1 617
384 8767; E-mail: jax@hsph.harvard.edu
Abstract: Objective: Compare wrist kinematics and typing force during computer
work across two workstations, one configured according to recommended
guidelines with the keyboard support surface flat and near resting elbow
height, the other according to users' actual setup and preference, with an
elevated, and positively tilted support surface. Participants: Twenty
participants completed a standard computer task at the two workstation
configurations. Methods: A thin profile force plate, placed under the
keyboard recorded keyboard reaction forces. Twin axis electro-goniometers (SG65
Biometrics Ltd, London, UK) affixed to the back of the right and left hand of
each subject continuously measured wrist extension/flexion and ulnar/radial
deviation. Results: Typing force and wrist kinematics were similar
between the two configurations with only 10th percentile ulnar
deviation for the right hand showing a borderline significant difference of
1° between the two configurations. Conclusion: Elevating and
tilting the input device support surface does not necessarily affect typing
force and kinematics of the wrist. The combination of the input device support
surface and user upper extremities form a complex kinematic system with several
degrees of freedom. Wrist postures during computer use are a function of
multiple factors other than simply keyboard tilt.
