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physical exposure for the hand and the wrist. The HAL is applicable to single-task jobs, although some
approaches have been attempted to extend its use in multiple-task situations. The RULA method (McA-
tamney and Corlett, 1993) is used to assess the postures of the neck, trunk, and upper limbs, muscular
effort, and the external loads on the body. This postural exposure assessment system has been used in
several different formats and adopted for use in many different types of industries (Lueder, 1996;
Hignett and McAtamney, 2000).
Time-based methods such as OWAS (Karhu et al., 1981), VIRA (Persson and Kilbom, 1983; and
Kilbom et al., 1986), ARBAN (Holzmann, 1982), and PEO (Fransson et al., 1991) require the analyst
to observe the job performance continuously or at specific time samples during the task performance.
The analyst records the exposure changes based on predefined categories, such as, hand with weight
versus hand without weight, and neck flexion between 0
. Observations
can be performed on-site with a computer or off-site where video-tapes are analyzed. Advantages of the
time-based methods are that they more closely represent the true exposure during the task performance.
The disadvantage is that it is time consuming and may also limit the number of exposure parameters that
an analyst can observe if the method is used on-site.
Video-based off-site techniques often use categorical scoring of body positions, movement frequency,
type of grip, and force based on either sampled or real-time recording (Karhu et al., 1977; Corlett et al.,
1979; Holzman-Voigt, 1979; Kemmlert and Kilbom, 1986; Keyserling, 1986; Armstrong et al., 1982). The
method employed by Armstrong et al. (1982), for example, sampled postures several times a second and
classified wrist postures into five categories: (1) neutral, (2) flexion, (3) extreme flexion, (4) extension,
and (5) extreme extension. In general, video-based analysis may be the most appropriate observational
method for risk factor quantification and definition of work activities for large-scale epidemiological
studies because it allows the analysts sufficient time to estimate the postures of the various body parts
and provides the possibility to reanalyze the data for quality control purpose.
With the availability of newer computer technologies, time studies of task performance and postural
analysis can now be carried out on computers. A recently developed multimedia video task analysis
(MVTA) system (Yen and Radwin, 1995) is able to set accurate time codes on videotapes and perform
time analysis on various time-based events (e.g., tasks, postures, and hand exertions). With its flexible
design, users can set their own parameters to be studied (e.g., tasks, wrist flexion and extension postures,
hand exertions) and define their own categories of the different parameters (e.g., for the parameter of task
with two levels: computer keyboarding and writing notes; for the parameter of wrist flexion
8
and 20
8
versus greater than 20
8
extension
/
with four categories: flexion 0 to 30
). A drawback
of this type of analysis is that the analyst has no control on the angles of observation, and has to depend
on the quality of the videotapes. Therefore, to obtain reliable and adequate exposure information, it is
important to take good-quality video. Another disadvantage with the computer-based observation
systems is that one cannot obtain direct measurements such as object weight and forces required to
operate a tool while the analyst is sitting in his or her laboratory. In contrast, when the observation is
done on-site, the analyst can most often communicate or interact with the operator to obtain the infor-
mation. Therefore, if the analysis is performed off-site, it is important to obtain the required information
on-site and be prepared for use in the off-site analysis.
Falling within the scope of observational field methods are methods based on workloads. These
methods define a system of quantifying an overall load score (Helliwell et al., 1992) or classify
workers into classes based on work levels (Nathan et al., 1993). The Strain Index developed by Moore
and Garg (1995) identified six risk factors, each given a categorical 1 to 5 score, that give an overall sever-
ity index (SI) score when multiplied together. This tool has been used in meatpacking and has shown
data that support its validity in predicting morbidity (Moore and Garg, 1995). Although the Strain
Index method was originally designed for single-task jobs, the authors have made attempts to extend
this method to multiple-task jobs.
Force quantification often presents a problem in observational methods. Hand force cannot be seen.
Consequently, it must be estimated, which can be achieved using several methods. A simple dichotomous
classification of either high or low force has commonly been used, typically using manipulation of a
8
, flexion
30
8
, extension 0 to 30
8
, and extension
30
8
.
.
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