Civil Engineering Reference
In-Depth Information
group was 11.3 errors per 100 typed words (SD
5.37), as compared to 15.3 (SD
3.14) for the
¼
¼
untrained subjects (p
0.039). Training on the Maltron keyboard significantly reduced the error
,
rate from 26.5 (SD
0.007). The fact that trained participants were
able to type at 89% of their baseline typing speed when using the Goldtouch keyboard constitutes
strong evidence that with additional experience alternative keyboards could easily replace the widespread
traditional design without any loss in productivity, or perhaps even a gain. Our results differ from those
reported by Treaster and Marras (2000), who noted a decrease of only 14% when typing on the Kinesis
TM
keyboard (similar design to Maltron). With regard to typing performance, Smith et al. (2000) noted
values similar to those recorded for the traditional keyboard after only 2 h of training on a split angle
keyboard. Previous research indicated that the initial decline in typing productivity has been recuperated
after 2 days of training.
For the Maltron keyboard, the more ergonomic working postures found in untrained participants (less
wrist ulnar deviation and extension) when compared with the traditional design, were maintained after
the training session. Working on the Goldtouch keyboard promoted mitigated ulnar deviation in both
untrained and trained groups. Although training decreased wrist repetition (number of wrist excursions
greater than 10
7.40) to 19.2 (SD
5.88) (p
¼
¼
,
0.05).
The 10% decrease in wrist repetition represents an important decrease in risk factors associated with
prolonged typing (e.g., tendon travel, tendon sheaths friction). After training, for one day of work the
decline in wrist repetition would be of 2400 movements per movement plane (5 repetitions
8
) with two to six repetitions per minute, the difference was not significant (p
.
/
min
8 h of work). For one hand (both ulnar-radial deviation and flexion-
extension planes) a total of approximately 4800 unnecessary wrist movements would be avoided
through training. For the Maltron keyboard, training induced values below 30 per minute, which is
the recommended highest acceptable frequency in a repetitive motion.
In terms of applied force, training significantly reduced the overall applied force for both Goldtouch
60 min per hour
(p
0.031) keyboards. The mean typing force was reduced by 58% for Gold-
touch and by 42% for the Maltron keyboard. For the Goldtouch keyboard the training session was
enough in order to reduce the typing force below the values for the conventional design (from 2.27 to
0.97 N, compared with 2.17 N recorded for the conventional one).
The decrease in overall applied force following training could be explained by hesitancy alleviation.
Working under time pressure, especially with keyboard designs totally different than the one subjects
are used to, spending more time in order to find the right keys leads to higher key stroke force (increased
finger velocities) when the key is found. Training makes devices more familiar, eliminating unnecessary
actions.
A synthesis of the effects of training on the studied variables is presented in Table 39.5.
0.022) and Maltron (p
,
,
39.5 Conclusions and Summary
Office work is associated with an elevated level of musculoskeletal risk factors. The upper extremity is
forced to be positioned in deviated postures with concomitant repetitive motions. Wrist neutral zone
should not be viewed as an arbitrary region of this particular range of motion. Low muscle activity
and CTP are present in activities carried out within these boundaries. The neutral zone varied
between 7
ulnar deviation. Significantly lower EMG muscle
activity was recorded while the wrist was positioned within neutral zone as compared to deviated
8
and 9
8
extension and between 5
8
and 7
8
TABLE 39.5 The Effect of Training on Studied Variables
Typing Performance
WPM
Keyboard
Wrist Posture Wrist Repetition
Applied Force
EMG Activity
Accuracy
Goldtouch
$
p
0.05
#
p
0.05
#
p
0.022
$
p
0.05
"
p
0.027
#
p
0.039
.
.
¼
.
¼
¼
Maltron
$
p
0.05
#
p
0.05
#
p
0.031
$
p
0.05
"
p
0.008
#
p
0.007
.
.
¼
.
¼
¼
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