Several keyboard design features (degree of split, degree of keyboard gable, degree of slope, key vertical height, key horizontal distance, and keyboard width) greatly influence forearm/wrist posture according to a study involving 105 subjects by Rempel et al. A neutral distal upper extremity posture – when considering wrist flexion/extension, wrist radial/ulnar deviation and forearm pronation/supination – was most promoted by a keyboard with a fixed moderate split (12º), moderate gable (14º), and no slope.
Study volunteers subjectively preferred three keyboard design styles:
· fixed moderate split (12º)/mild gable (8º)/no slope
· fixed moderate split (12º)/moderate gable(14º)/no slope
· fixed moderate split (12º)/moderate gable(14º)/mild slope(-7º)
The conventional keyboard design was associated with the fastest typing speed while the conventional laptop was least preferred design style.
Study Design
Subjects were recruited from a university campus (45 percent) and local temporary employment agency (55 percent) who:
1. could touch type 40 words per minute
2. had at least one week of experience using a split keyboard (a volunteer without this background was allowed to be included if a 4 hour intensive typing task on a split keyboard was performed several days prior to the study)
3. were void of current head, neck, back or arm injuries
4. had no difficulty performing keyboarding for an entire day.
Nearly 70 percent of the included subjects had used a split keyboard for greater than one week.
Six keyboards of varying design were tested. Keyboard styles are presented in Table 1.
|
Keyboard
Design
|
Model
|
Split
Angle
(deg)
|
Gable
Angle
(deg)
|
Slope
(deg)
|
Height
(mm)
|
Horizontal
(mm)
|
D to K
(mm)
|
|
Conventional
Straight Keyboard
|
Dell Model No SK-8110
|
0
|
0
|
0
|
30
|
67
|
95
|
|
Conventional
Laptop
|
Dell Latitude C800, Model No. PP01X
|
0
|
0
|
0
|
35
|
166
|
94
|
|
Fixed mild split; no gable; no slope
|
Microsoft Comfort Curve Keyboard 2000
|
6
|
0
|
0
|
20
|
87
|
106
|
|
Fixed moderate split; mild gable; no slope
|
Microsoft Natural Elite
|
12
|
8
|
0
|
41
|
132
|
144
|
|
Fixed moderate split; moderate gable; no slope
|
Microsoft Natural Ergonomic Keyboard 4000
|
12
|
14
|
0
|
36
|
151
|
138
|
|
Fixed moderate split; moderate gable; mild slope
|
Microsoft Natural Ergonomic Keyboard 4000 with reverse slope attachment
|
12
|
14
|
– 7
|
49
|
149
|
138
|
Height = distance in mm from the table surface to the top center of the “D” key.
Horizontal = distance in mm from the front edge of the keyboard closest to the user to the center of the “D” key.
D to K = distance in mm between the centers of the “D” and “K” keys.
Table 1: Keyboard styles utilized in the study.
The study was performed in a laboratory setting using a chair (Steelcase Leap without arm supports) that was adjusted to fit/support the volunteer’s anthropometry. The keyboard support surface was adjusted to the volunteer’s elbow height. The monitor was placed vertically such that the center of the screen was 15 degrees below the horizontal eye view. The keyboard was positioned and secured with double-sided tape with the home row 16.0 cm from the front edge of the support surface.
Forearm/wrist positioning was recorded through the use of four plastic plates containing infrared light emitting diodes (IRED) placed over the dorsal aspect of each subject’s hands and forearms. An IRED was also placed over the lateral epicondyle bilaterally.
Subjects practiced on the 3 gabled keyboards for 10 to 20 minutes. In a random fashion, 1 of the 6 keyboards was chosen to begin the typing task. Five minutes into task, posture data was recorded for 5 minutes. Net typing speed and errors were measured. After a keyboard was tested, a comfort questionnaire was completed. The next keyboard was tested following a 3-minute rest.
Once all 6 keyboards were tested, the subjects compared the models relative to ease of use, accuracy, speed, comfort, overall opinion. The volunteers also identified their preferred model.
Other Findings
For wrist flexion/extension, neutral position was most closely assumed when using the:
· Conventional laptop
· Fixed moderate split, moderate gable, no slope keyboard
· Fixed moderate split, moderate gable, mild slope keyboard
For wrist radial/ulnar deviation, neutral position was most closely assumed when using the:
· Fixed moderate split, mild gable, no slope keyboard
· Fixed moderate split, moderate gable, no slope keyboard
For forearm pronation/supination, neutral position was most closely assumed when using the:
· Fixed moderate split, moderate gable, mild slope keyboard
The largest degree of wrist extension was seen when subjects used the conventional straight and the fixed mild split, no gable, no slope keyboards. The greatest ulnar deviation and greatest pronation position was recorded with use of the conventional laptop and conventional straight keyboard, respectively.
Study Limitations
Reservations effecting of this research include:
1. the brief exposure many subjects had to split/gabled/sloped keyboards prior to the study; this may have effected typing speed
2. the tendency of individuals to prefer a keyboard with which they are most accustomed.
Article Title: The effect of six keyboard designs on wrist and forearm postures
Publication: Applied Ergonomics 38: 293-298, 2007
Authors: D Rempel, A Barr, D Brafman, and E Young
This article originally appeared in The Ergonomics Report™ on 2007-07-06.