Civil Engineering Reference
In-Depth Information
TABLE 47.10 Maximum Acceptable Forces for Female Wrist Flexion (Power Grip) (N)
Repetition rate
Percent of population
2
/
min
5
/
min
10
/
min
15
/
min
20
/
min
90
14.9
14.9
13.5
12.0
10.2
75
23.2
23.2
20.9
18.6
15.8
50
32.3
32.3
29.0
26.0
22.1
25
41.5
41.5
37.2
33.5
28.4
10
49.8
49.8
44.6
40.1
34.0
Source: Reprinted from Snook, S. H. and Ciriello, V. M. Journal of Occupational Medicine, 16, 527-534, 1974. With
permission.
duration would need to be reduced, or factors such as wrist deviation would need to be modified to
increase the acceptability of a task.
While Fernandez and his colleagues chose frequency as the variable that subjects manipulate, Snook
et al.
14
chose force as the manipulated variable. Also, Snook et al.
14
used a 7-h adjustment period
which was much longer than the shorter (20-25 min) period used in the studies cited earlier.
Snook et al.
14
studied tasks requiring wrist flexion with a power grasp, wrist flexion with a pinch
grip, and extension with a power grasp. Frequencies between 2 and 20 repetitive motions per minute
were studied. Subjects adjusted wrist torque during the experiment by manipulating the resistance
offered by a magnetic particle brake. Aside from reporting the torques, forces were also reported
which were computed by dividing the torques by the moment arms. The forces are reported in
Table 47.10 through Table 47.12.
Ciriello et al.
46
reported the results of a psychophysical study of six hand movements. In addition to
the motions studied by Snook et al.,
14
wrist extension with a pinch grip, ulnar deviation with a power
grip, and a handgrip task (power grip) were studied. Ciriello et al.
47
investigated ulnar deviation with
a power grip and the handgrip task, but included clockwise screwdriver motions using 31 and 40 mm
handles and a 39 mm yoke handle. Counterclockwise screwdriver motions with a 31 mm handle
completed the experimental conditions. Subjects selected 14-24% of maximum isometric torque for
the different motions, at different frequencies.
The data reported by Snook et al.
14
and Ciriello et al.
46,47
would be applied in a manner similar to that
described earlier in this section. However, these data are more generic than some of the data collected by
Fernandez and his colleagues. The Ciriello et al.
47
data contain a mix of generic and task-specific data.
For example, the data collected by Snook et al.
14
do not apply only to specific tasks such as drilling,
as do some of the data from other studies mentioned.
37 - 40
Krawczyk et al.
48
presented preferred weights for manual transfer tasks for transfer distances of 0.5 and
1.0 m and frequencies between 10 and 30 transfers per minute for an 8 h work duration. Thus, depending
on the situation, one could adjust frequency or transfer distance for a particular weight of object being
transferred.
TABLE 47.11 Maximum Acceptable Forces for Female Wrist Flexion (Pinch Grip) (N)
Repetition rate
Percent of population
2
min
5
min
10
min
15
min
20
min
/
/
/
/
/
90
9.2
8.5
7.4
7.4
6.0
75
14.2
13.2
11.5
11.5
9.3
75
19.8
18.4
16.0
16.0
12.9
75
25.4
23.6
20.6
20.6
16.6
10
30.5
28.2
24.6
24.6
19.8
Source: Reprinted from Snook, S. H. and Ciriello, V. M. Journal of Occupational Medicine, 16, 527-534, 1974. With
permission.
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