제 목 : Research Helps Explain Shoulder Pain
일 자 : 1997년 06월
제공처 : Safety ＆ health
Researchers at Denmark's National Institute of Occupational Health
have been studying the physical causes of shoulder pain which cano affect
slaughterhouse workers, sewing-machine operators and others involved
in repetitive tasks that require the arms to be raised for long periods.
The researchers measured the response of test subjects' muscles to
simulated repetitive work. This showed that some shoulder muscle
fibers remained fully active for the entire period of use of the shoulder
area, even when the workload was very light. It helps explain why even
light work can produce shoulder pain, the researchers believe.
Light work also can cause muscle injury because the fatigue signals
that come from the muscles are easier to ignore.
"If you perform heavy work such as lifting boxes, you can feel when
you are tired and can't continue. With light repetitive work, although
you feel tired and your muscles may be burning, you are still able to
continue working," says researcher Bente R. Jenson.
Shoulder muscles take longer to recover from effort. Ninety-five per-
cent of the most important areas of the muscle were still active afrer
a half-hour break from half an hour of light work. By comparison, only
66percent of arm muscles were still active afrer the same workload and
rest break.
The researchers also believe that the magnitude of shifts in working
position needed to give loaded muscles a rest has been underestimated.
A small change in the angle of hand, arm or shoulder to a position
which is only slightly different may still involve the same muscle
fibers used in the previous position.
The mechanisms that connect muscle injury to work organization
and other nonphysical factors are not fully understood, says Jenson.
"In this study, we have only considered the physical part of shoulder
muscle injury," she says. "Other studies have shown that work pace
and precision work will further increase muscle activity. Psychosocial
pressures may make it more difficult to relax your muscles."
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