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work-related MSK disorders (see appendix B in NIOSH report). In the more resent NRC
IOM Panel
report, individual factors are thought to affect personal responses to workplace exposures and tend to
be thought of as physiological and psychological attributes in contrast to biomechanical characteristics
(NRC
/
IOM Panel on Musculoskeletal Disorders, 2001).
Conceptualizing the nature and meaning of individual factors therefore remains a challenge. The aim
of this article is to share an approach to consideration of individual factors in MSK disorders. It draws on
experience of the first author as a primary care physician, occupational medicine
/
community medicine
/
specialist, and clinical
population epidemiologist. Given the multiple specific questions that might be
involved, our citation of evidence is illustrative rather than comprehensive, making reference to systema-
tic reviews when available or individual studies when useful, and pointing to complementary treatment
in other articles in this volume when appropriate. We start by exploring what individual factors rep-
resent. We go on to consider the similar and different roles of individual factors as they operate in the
course of an MSK disorder and the ways that their contribution can be estimated. We then note both
the rationale for consideration of individual factors and the directions we might go in considering indi-
vidual factors in our joint efforts to reduce the burden of MSK disability.
/
19.2 What Do Individual Factors Associated with
MSK Disorders Represent?
People are essentially unique, resulting in distributions of most factors that we measure at the level of the
individual person. Hence variation that we might attribute to individuals is the rule rather than the
exception. However, the source of the variation that we might observe across individuals may be concep-
tualized in multiple ways (see Table 19.1). For heuristic purposes, we can group these into those that are
potentially work-related, those that are best understood as concurrent exposures, and those that can be
thought of as “vulnerabilities.”
19.2.1 Work-Related Factors
Gender in most societies is associated with differential work roles for women and men (Messing et al.,
1995). The traditional division of labor into “light” and “heavy” work is particularly apparent in the
manufacturing and service sector, where women are typically assigned to jobs characterized by repetitive
movements, rapid work rate, involving little force, whereas men are often found working in tasks
with more extreme physical demands, but with less repetitiveness and often performed at slower
speed (Messing et al., 1998). Where men have been placed in traditional women's working conditions
in poultry slaughterhouses, they reported similar health symptoms as women coworkers (Mergler
et al., 1987).
Social and age stratification in psychosocial exposures and associated health effects are also apparent
(Brisson et al., 2001; Montreuil et al., 1996). Yet age is a difficult variable to de-construct. Is it a measure
of differential exposure (lighter jobs for older workers), cumulative exposure, declining tissue tolerance,
greater experience and skill, other factors, or a combination? Research in slaughterhouses found that
inexperienced workers had to invest more physical effort for the same task (knife-sharpening) compared
to workers with more training (Vezina et al., 1996, 2000). These differences in work procedures in turn
lead to disproportionately more health problems among inexperienced workers.
Varying individual workstyles can put certain workers at differential risk for developing MSK dis-
orders. Different methods of lifting loads and spine stabilization have been observed in laboratory,
field and clinical settings, which, when altered, can reduce low back symptoms (McGill, 2001). In a
group of sign language interpreters, those with a tendency to work with pain to ensure work quality
were at greater risk of having upper extremity symptoms (Feuerstein et al., 1997).
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