Affiliations: Department of Industrial and Manufacturing
Engineering, Kettering University, Flint, MI, USA | Department of Environmental Health, Harvard School of
Public Health, Boston, MA, USA | Synaptics, Santa Clara, CA, USA | Microsoft Corporation, Richmond, WA, USA | Department of Physical Therapy, Bouvé College
of Health Sciences, Northeastern University, Boston, MA, USA | Brigham and Women's Hospital, Boston, MA, USA
Note: [] Address for correspondence: Jack T Dennerlein, Northeastern
University, Department of Physical Therapy, 6 Robinson Hall, 360 Huntington
Ave, Boston, MA 02115, USA. Tel.: +1 617 373 5428; E-mail:
j.dennerlein@neu.edu
Abstract: BACKGROUND: Due to its rapid growth in popularity, there is an
imminent need for ergonomic evaluation of the touch-screen tablet computing
form-factor. OBJECTIVE: The aim of this study was to assess postures of the
shoulders and wrists and their associated muscle activity during touch-screen
tablet use. METHODS: Fifteen experienced adult tablet users completed a set of
simulated software tasks on two media tablets in a total of seven user
configurations. Configurations consisted of a combination of a support
condition (held with one hand, two hands or in a case), a location (on the lap
or table surface), and a software task (web browsing, email, and game).
Shoulder postures were measured by using an infra-red LED marker based motion
analysis system, wrist postures by electro-goniometry, and shoulder (upper
trapezius and anterior deltoid) and forearm (flexor carpi radialis, flexor carp
ulnaris, and extensor radialis) muscle activity by surface
electromyography. RESULTS: Postures and muscle activity for the wrist significantly
varied across configurations and between hands, but not across the two tablets
tested. Wrist extension was high for all configurations and particularly for
the dominant hand when a tablet was placed on the lap (mean=38°). Software
tasks involving the virtual keyboard (e-mailing) corresponded to higher wrist
extensor muscle activity (50th percentile=9.5% MVC) and wrist flexion/extension
acceleration (mean=322°/s^{2}). High levels of wrist
radial deviation were observed for the non-dominant hand when it was used to
tilt and hold the tablet (mean=13°). Observed differences in posture and
muscle activity of the shoulder were driven by tablet location. CONCLUSION: Touch-screen tablet users are exposed to extreme wrist
postures that are less neutral than other computing technologies and may be at
greater risk of developing musculoskeletal symptoms. Tablets should be placed
in cases or stands that adjust the tilt of the screen rather than supporting
and tilting the tablet with only one hand.
Keywords: Slate computing, media tablets, mobile computing
