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degree of confidence, that there is a strong relationship between certain work tasks and the risk of musculoskeletal disorders.

    4. What is the relative contribution of any causal factors identified in the literature to the development of such conditions in (a) the general population, (b) specific industries, and (c) specific occupational groups?

A. Individual Risk Factors

Because 80 percent of the American adult population works, it is difficult to define a “general population” that is different from the working population as a whole. The known risk factors for musculoskeletal disorders include the following:

Age—Advancing age is associated with more spinal complaints, hand pain, and other upper extremity pain, e.g., shoulder pain. Beyond the age of 60, these complaints increase more rapidly in women than men. The explanation for spinal pain is probably the greater frequency of osteoporosis in women than in men. The explanation for hand pain is probably the greater prevalence of osteoarthritis affecting women. However, other specific musculoskeletal syndromes do not show this trend. For example, the mean age for symptomatic presentation of lumbar disc herniation is 42 years; thereafter, there is a fairly rapid decline in symptoms of that disorder.

Gender—As noted above, there are gender differences in some musculoskeletal disorders, most particularly spinal pain due to osteoporosis, which is more commonly found in women than in men, and hand pain due to osteoarthritis, for which there appears to be a genetic determinant with increased incidence in daughters of affected mothers.

Healthy lifestyles—There is a general belief that the physically fit are at lower risk for musculoskeletal disorders; there are few studies, however, that have shown a scientific basis for that assertion. There is evidence that reduced aerobic capacity is associated with some musculoskeletal disorders, specifically low back pain and, possibly, lumbar disc herniations are more common in cigarette smokers. Obesity, defined as the top fifth quintile of weight, is also associated with a greater risk of back pain. There currently is little evidence that reduction of smoking or weight reduction reduces the risk.

Other exposures—Whole-body vibration from motor vehicles has been associated with an increase in risk for low back pain and lumbar disc

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