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Thumb motor performance varies with thumb and wrist posture during single-handed mobile phone use.

Authors
Trudeau-MB; Young-JG; Jindrich-DL; Dennerlein-JT
Source
J Biomech 2012 Sep; 45(14):2349-2354
NIOSHTIC No.
20042096
Abstract
Design features of mobile computing technology such as device size and key location may affect thumb motor performance during single-handed use. Since single-handed use requires the thumb posture to vary with key location, we hypothesize that motor performance is associated with thumb and wrist joint postures. A repeated measures laboratory experiment of 10 right-handed participants measured thumb and wrist joint postures during reciprocal tapping tasks between two keys for different key pairs among 12 emulated keys. Fitts' effective index of performance and joint postures at contact with each key were averaged across trials for each key. Thumb motor performance varied for different keys, with poorest performances being associated with excessive thumb flexion such as when tapping on keys closest to the base of the thumb in the bottom right corner of the phone. Motor performance was greatest when the thumb was in a typical resting posture, neither significantly flexed nor fully extended with slight CMC joint abduction and supination, such as when tapping on keys located in the top right and middle left areas on the phone. Grip was also significantly affected by key location, with the most extreme differences being between the top left and bottom right corners of the phone. These results suggest that keypad designs aimed at promoting performance for single-handed use should avoid placing frequently used functions and keys close to the base of the thumb and instead should consider key locations that require a thumb posture away from its limits in flexion/extension, as these postures promote motor performance.
Keywords
Biomechanics; Muscle-function; Musculoskeletal-system; Physical-capacity; Physical-reactions; Physiological-factors; Physiological-function; Author Keywords: biomechanics; Fitts' law; motor control; texting; keypad interface
Contact
Jack T. Dennerlein, Harvard School of Public Health, Department of Environmental Health, 401 Park Drive, Room 404L, Boston, MA 02215
CODEN
JBMCB5
Publication Date
20120921
Document Type
Journal Article
Email Address
jax@hsph.harvard.edu
Funding Type
Grant
Fiscal Year
2012
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-T42-OH-008416
Issue of Publication
14
ISSN
0021-9290
Source Name
Journal of Biomechanics
State
MA
Performing Organization
Harvard School of Public Health
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