Keyswitch orientation can reduce finger joint torques during tapping on a computer keyswitch. 2006

Aruna D Balakrishnan, and Devin L Jindrich, and Jack T Dennerlein
Harvard School of Public Health, Boston, Massachusetts 02115, USA.

OBJECTIVE To examine the effects of keyswitch orientation on joint torques. BACKGROUND The fingertip produces primarily vertical forces during single-finger tapping on a computer keyswitch. However, horizontal force components within the sagittal plane of the finger could reduce net joint torques. METHODS Eleven participants tapped on a keyswitch oriented in three directions: vertical, tilted 30 degrees such that when pressed it moved away from the user (similar to a positive-tilt keyboard), and tilted 30 degrees such that when pressed it moved toward the user (similar to a negative-tilt keyboard). Participants also tapped on a prototype cantilever keyswitch design in which the key cap moves along the arc of a bending beam gradually away from the user. Miniature electro-optical goniometers measured the finger posture, and a two-axis force sensor measured fingertip forces. RESULTS Tapping on a keyswitch oriented such that it moves away from the user when pressed reduced net joint torques by 47% relative to tapping on a vertically orientated keyswitch and by 56% relative to tapping on a keyswitch oriented toward the user, whereas the cantilever design resulted in 14% decreases in net joint torque relative to the vertical orientation. CONCLUSIONS Reductions of torques resulted from decreasing the moment arm of the fingertip force about the joints. CONCLUSIONS Keyboard design should incorporate keyswitch mechanism angles along with other postural and geometric constraints to reduce exposure of the finger joints and muscles to force during typing.

UI MeSH Term Description Entries
D008297 Male Males
D003201 Computers Programmable electronic devices designed to accept data, perform prescribed mathematical and logical operations at high speed, and display the results of these operations. Calculators, Programmable,Computer Hardware,Computers, Digital,Hardware, Computer,Calculator, Programmable,Computer,Computer, Digital,Digital Computer,Digital Computers,Programmable Calculator,Programmable Calculators
D005260 Female Females
D005384 Finger Joint The articulation between the head of one phalanx and the base of the one distal to it, in each finger. Interphalangeal Joint of Hand,Interphalangeal Joint of Finger,Finger Interphalangeal Joint,Finger Interphalangeal Joints,Finger Joints,Hand Interphalangeal Joint,Hand Interphalangeal Joints,Joint, Finger,Joints, Finger
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000328 Adult A person having attained full growth or maturity. Adults are of 19 through 44 years of age. For a person between 19 and 24 years of age, YOUNG ADULT is available. Adults
D013647 Task Performance and Analysis The detailed examination of observable activity or behavior associated with the execution or completion of a required function or unit of work. Critical Incident Technique,Critical Incident Technic,Task Performance,Task Performance, Analysis,Critical Incident Technics,Critical Incident Techniques,Incident Technic, Critical,Incident Technics, Critical,Incident Technique, Critical,Incident Techniques, Critical,Performance, Analysis Task,Performance, Task,Performances, Analysis Task,Performances, Task,Task Performances,Task Performances, Analysis,Technic, Critical Incident,Technics, Critical Incident,Technique, Critical Incident,Techniques, Critical Incident
D014481 United States A country in NORTH AMERICA between CANADA and MEXICO.
D019415 Torque The rotational force about an axis that is equal to the product of a force times the distance from the axis where the force is applied. Torques

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