Civil Engineering Reference
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plane are similar to velocities measured in workers involved in industrial activities with great risk for
CTS. Nerve compression due to thickening of the flexor tendon sheaths has been proven by Yamaguchi
et al. (1965) who found greater fibrosis and edema in the tendon sheaths in CTS patients compared with
controls. Highest velocity and accelerations occurred in flexion
extension and radial
ulnar deviation
/
/
movements (Serina et al., 1999).
39.4.2 The Effect of Alternative Design on CTS Risk Factors
Previous research and design efforts to reduce the risk factors level have focused on re-shaping the
standard keyboard, or making it more adjustable, while keeping its basic design and QWERTY layout.
This would ensure a smooth transition to the new keyboard design. Improved hand and arm postures,
without the need for learning a whole new typing skill, are achieved. Split keyboards are the most
commonly seen by most and are typically the least expensive of the alternative keyboards. They have a
set horizontal split angle and possibly a slight center raise or “tenting” of the left and right hand key
segments. They have been used in many studies (Hedge and Powers, 1995; Harvey and Peper, 1997;
Smith et al., 1998; Marklin et al., 1999; Lincoln et al., 2000; Marklin and Simoneau, 2001) along with
QWERTY or other alternative keyboards.
Smith et al. (1998), in a comparative study between split and conventional keyboards, noted that a split
keyboard allows the hand, wrist and arms to be maintained in more neutral positions. Both right and left
ulnar deviation and pronation were reduced. Keeping the wrist within the neutral zone for a longer
period of time, promotes decreased force applied on carpal bones, ligaments, and tendon sheaths
(Armstrong and Chaffin, 1979; Armstrong et al., 1984; Marklin et al., 1999). Mitigated CTP, the
major trigger for CTS follows. Marklin and Simoneau (2001), while assessing split computer keyboards,
showed that wrist ulnar deviation ranged from 7.0
8
to 8.5
8
for the left wrist and from 2.7
8
to 5.0
8
for the
right wrist for alternative keyboards as compared to 15
for both hands for conventional keyboards.
Using the split keyboard under correct settings would ensure a reduction in ulnar deviation equal to half
of the split angle. Another advantage of split keyboards have been cited by Treaster and Marras (2000)
who determined that alternative keyboard design can affect tendon travel by as much as 11%, reducing
the thickening process of the tendon sheaths.
When using a split keyboard the problem of wrist-extended posture is still present (Hedge and Powers,
1995). Also, placing the mouse in a more lateral position will require elevated arm abduction (Harvey
and Peper, 1997). Treaster and Marras (2000) noted that volunteers failed to set the split keyboard in
order to reduce the tendon travel. Educational and ergonomic programs are needed to increase the
awareness among VDT users regarding the safe postures that are required while typing.
Negative slope keyboard support (NSKS) reduces the wrist extension problem mitigating it from 13
8
-30
8
8
extension to 1.2
flexion (Hedge and Powers, 1995). Subjects responded very favorably to the NSKS
system. A downside is that the ulnar deviation remains the same or it is even greater because of the
active process of fitting the finger to reach the same point. Despite the fact that the keyboards of
many computers are flat, almost none of the conventional computer keyboards used on a flat work
surface actually has a 0
8
8
slope, and therefore, a much more ergonomic keyboard would be an NSKS
with a split angle.
Participants have had the ability to rapidly adapt to the changes in keyboard design (Hedge and
Powers, 1995; Smith et al., 1998; Marklin et al., 1999; Zecevic et al., 2000; Marklin and Simoneau,
2001). The average speed for alternative keyboards was reduced with 10% when compared to the
speed for conventional keyboards (Marklin et al., 1999; Marklin and Simoneau, 2001). The resultant
typing performance is even more remarkable if we take into account the training time, which was
very short (Smith et al., 1998). Although the aforementioned studies have not had too many subjects,
and not all the alternative designs have been included, there is sufficient evidence to support the super-
iority of alternative keyboards over conventional ones.
The effect of alternative keyboard design on typing variables have been assessed by Fagarasanu
et al. (2004b) who conducted an experiment in which wrist motion, forearm muscle activity, applied
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