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for as long as possible, and if estimates of discomfort level were made at intervals during the holding
time, the growth of discomfort was linearly related to holding time regardless of the level of force
being exerted (Corrlet, 1995). Therefore, it was concluded that perception of discomfort level can be
used as a linear scale. In this technique the severity of discomfort is evaluated on a five- or seven-
point ordinal scale anchored at 0 and 5(7) categories by “no discomfort” and “extreme discomfort.”
In order to identify the body areas where discomfort is experienced the body map divided into seg-
ments is used. The original body chart used in Corlett and Bishop (1976) has been modified by many
researchers to fit their particular purposes (Olendorf and Drury 2001; Drury et al., 1989). Coury and
Drury (1982) and Drury et al. (1989) developed three summary measures for the Body Part Discomfort
Scale: BPD frequency (BPDF), BPD severity (BPDS), and BDP frequency severity (BPDFS). BPDF is cal-
culated as the number of body parts rated greater than zero, whereas BPDS is the average of all nonzero
ratings. BPDFS is the product of the BPDF and BPDS.
The Body Part Discomfort Scale (Corrlett and Bishop, 1976) has been validated in a many studies. Sig-
nificant relationship was found between the applied biomechanical torque and discomfort (Boussenna
et al., 1982). The Boussenna et al. (1982) study also supported relationship between holding time and
perceived discomfort level, that is postures that caused greater discomfort than others led to shorter
holding times. Jung and Choe (1996) demonstrated that a psychophysical scale of discomfort correctly
reflects physiological muscle activity obtained with EMG recordings. The cross-validation of this tech-
nique with RPE scale and OWAS showed high intercorrelation of results (Drury et al., 1989; Liao and
Drury, 2000; Olendorf and Drury, 2001). The reliability of body discomfort scale was demonstrated
with high intersubject agreement correlation in the study on the postural loading effect at joints
(Boussenna et al., 1982). However, the research results on sensitivity of the Body Part Discomfort
Scale are equivocal. Bonney et al. (1990) revealed that perceived discomfort discriminate 20
changes
in back postures from one another. In the study by Kumar et al. (1999), the BDPR was unable to differ-
entiate between task variables, in comparison to RPE and visual scale (VS) that were sensitive to changes
in the lifting tasks, which were of a short duration, continuous, and not biomechanically demanding.
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37.3.3.2 Nordic Questionnaire for the Musculoskeletal Symptoms
The Nordic questionnaire (NQ) consists of structured, forced binary or multiple-choice questions used
to indicate general and specific information regarding pain in various regions of the body (Kuorinka
et al., 1987). It can be used in self-assessment and in interviews. The questionnaire is enhanced with
generic body diagrams used for identifying painful regions of the body. There are two types of the
questionnaire: (1) a general questionnaire, and (2) specific ones focused on the low back and neck
/
shoulders. The main purpose of the questionnaire is the screening of musculoskeletal disorders in
the context of ergonomics. The localization of symptoms may reveal their causes in terms of loading
analyzed in reference to the daily activities, job tasks, and work environment (Dickinson et al., 1992).
37.4 Subjective Scales of Mental Workload Measurement
37.4.1 NASA Task Load Index
The NASATask Load Index (TLX) (Hart and Staveland, 1988) is a multidimensional subjective workload
rating technique. In TLX workload is defined as the “cost incurred by human operators to achieve a
specific level of performance.” (Rehman, 1995). The NASA TLX uses six dimensions to assess subjective
workload: (1) mental demand, (2) physical demand, (3) temporal demand, (4) performance, (5) effort,
and (6) frustration. Rating scales description is presented in Table 37.5. Each of the dimensions is rated
on the 20-step bipolar scale (Figure 37.1).
The overall workload score is based on the weighted average of ratings on the six workload dimensions.
The evaluation procedure with TLX consists of two stages. First, during the scale development procedure,
each subject evaluates all possible paired comparisons of the six dimensions, in order to specify the
member of each pair that has larger contribution to the workload of assessed task. Values obtained
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