Civil Engineering Reference
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both left and right sides (p
0.001). The PST keyboard required 9
8
-13
8
more ulnar deviation than
,
Maltron and Goldtouch keyboards for both LUR and RUR planes (p
0.001). The Goldtouch keyboard
design forced 80% of subjects to type with the left or right wrist in greater than 20
,
extension as
compared to 70% for the conventional and PST and 30% for Maltron. Within keyboards, no significant
differences were found between sides for all four planes. In order to reduce the risk of musculoskeletal
problems at this level, wrist extension should be lowered at 5
8
8
-10
8
. A split design QWERTY layout
with 25
lateral slope, and horizontal or negative slope is needed. While lateral
slope tends to decrease forearm pronation, it also reduces typing productivity and user's acceptance.
The reduction in both ulnar deviation and shoulder external rotation due to split angle design
promote a safe forearm pronation while typing.
In terms of wrist excursions greater than 10
8
-30
8
split angle, 0
8
, Maltron caused decreased wrist repetition for REF, LUR,
and RUR planes. Table 39.2 presents the repetitive values for all four keyboards tested. No significant
differences were found between the conventional, Goldtouch, and PST keyboards for all four movement
planes. For the Maltron keyboard, the key-column vertical curvature and the thumb keys for Enter, Back-
space, Delete, and other frequently used keys reduced the hand movement in the extension-flexion plane.
For the ulnar-radial deviation plane, the wrist repetitive movements over 10
8
were reduced by the pre-
sence of the central numeric pad, which could be used by either hand, as preferred. Also, straight vertical
key-columns reduced wrist excursions. Some of these design features should be further evaluated and, if
valid, adopted by other keyboards.
Compared with the conventional keyboard, only Maltron had a statistically significant difference in
applied force (p
8
0.001). The mean typing force for participants using the conventional keyboard
,
was 1.91 N (SD
1.05), as compared to Maltron (M
5.84; SD
4.16). The mean applied typing
¼
¼
¼
forces for Goldtouch and PST were 0.97 N (SD
0.85), in that order, which
were 4.87 and 4.56 N, respectively, lower than the Maltron's average force (p
0.52) and 1.28 N (SD
¼
¼
0.001). The overall
applied typing force recorded while using the conventional and Maltron keyboards exceeded the
ANSI
,
HFS recommendations (0.5-1.5 N). These results are similar to those of Rempel et al. (1994),
who using a piezoelectric load cell determined that the subject's mean peak force ranged between 1.6
and 5.3 N. The differences in overall typing force can be explained by important variations in keyswitch
characteristics (key travel distance, over travel distance, stiffness, and keyswitch make force).
In terms of EMG muscle activity while typing, no significant differences were found between the six
recorded muscles (ECU, FCR, FCU bilaterally) for all four keyboards.
Table 39.3 presents the average values for typing speed and accuracy for each keyboard. The Maltron
keyboard was associated with significantly lower performance compared to other three keyboards for
both typing speed and error rate (p
/
0.001). While the conventional and PST keyboard were statistically
similar in terms of accuracy, Goldtouch keyboard showed significantly higher error rate than the conven-
tional, with 89% level of confidence. For the Maltron keyboard, the productivity was significantly
reduced (58% decrease in typing speed and 149% increase in error rate, when compared to the conven-
tional keyboard). On the Goldtouch keyboard, subjects reached 86% and on the PST keyboard 90%, of
their typing speed on the traditional keyboard. Also, the error rate for these keyboards was statistically
identical when compared to the conventional design. The decrease in productivity of 58% for the
,
TABLE 39.2 Mean Values and Standard Deviations for Wrist Repetition
.
10
8
Per Minute for All
Planes and Keyboards
Movement Plane
Keyboard
LEF
REF
LUR
RUR
Conventional
51 (13)
44 (15)
9 (3)
12 (5)
Goldtouch
43 (10)
39 (14)
12 (6)
10 (5)
Maltron
26 (8)
29 (12)
7 (3)
10 (5)
PST
46 (14)
41 (12)
9 (6)
12 (4)
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