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with low back pain in industry (Punnet et al., 1991; Marras et al., 1993, 1995; Ono et al., 1997; Brulin
et al., 1998; Josephson et al., 1998; Norman et al., 1998; Wickstrom and Pentti, 1998; Ozguler et al.,
2000). Further, Figure 28.2 also provides indirect evidence of the importance of trunk flexion by having
greater compression and anterior-posterior shear forces as the lift origin becomes lower (e.g., knee or
floor height). It would be expected that these lower regions would have more trunk flexion (based on pre-
vious literature).
Awkward postures (e.g., lateral flexion, twisting, and combination of flexion with twisting) also pose a
risk to workers with respect to low back pain (Andersson, 1981; Kelsey and Golden, 1988; Hales and
Bernard, 1996; Ferguson and Marras, 1997; Hoogendoorn et al., 1999). One factor that influences the
awkward postures is task asymmetry — producing greater lateral flexion and twisting (Ferguson et al.,
1992; Plamondon et al., 1995; Allread et al., 1996; Kingma et al., 1998; Marras and Davis, 1998;
Granata et al., 1999). Task asymmetry is the location of the object (or box) being lifted relative to the
midsagittal plane of the individual at the beginning or at the end of the lift (NIOSH, 1993). Increases
in nonsagittal plane motion (lateral and twist) will typically accompany more asymmetric tasks since
the box is located away from the midline of the sagittal plane, causing the individual to twist and
bend sideways. However, the magnitude of off-plane motion may be minimized by lower extremity
compensation (e.g., moving of feet or twisting of hips).
The posture of the worker can be quantified by several methods with varying levels of accuracy and
resource requirements (cost, time, effort, and knowledge) (Burdorf et al., 1997). The simplest method
is using a checklist or questionnaire that identifies designated regions (see Figure 28.3 for an
example). The basic checklist method uses diagrams as a reference to identify how far an individual
flexes forward, flexes laterally, or twists. One useful aid is to videotape the worker performing the job
so that repeated evaluations of the postures may be made. The drawback of this method is the subjectivity
or the ability to distinguish the actual posture of the individual, particularly twist postures. These
methods are effective for more gross assessment of posture.
For more accurate quantification of the posture, goniometers (also referred to as electrogoniometers
or potentiometers) measure joint position; in this case, the lower back. There are several forms of low
back goniometric systems (e.g., lumbar motion monitor, Isotechnologies Back Tracker) that are commer-
cially available, but each requires substantial monetary resources and expertise in application. One
system, the lumbar motion monitor (LMM), has been validated with a large industrial database that
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0°
20°
20°
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60°
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L3/L4
FIGURE 28.3 One example of checklist diagrams for posture: Trunk flexion diagram from REBA checklist.
(Adapted from Hignett and McAtamney, 2000. With permission.)
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