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Bowen D.J., Purswell J.L., Schlegel R.E. and Purswell
J.P.
School of Industrial Engineering, University of Oklahoma,
Norman, OK
Introduction: The authors of this study note that the tension
of a back support has not been part of previous studies, including
those reviewed by NIOSH in its 1994 back belt booklet. They suggest
this lack of control of belt tension may contribute to the controversy
regarding back supports. Specifically, this study tried to determine:
· the wearer-preferred tension in an elastic back support
during repetitive lifting, and
· the psychophysical lifting limit for subjects with
no belt, a belt at minimal tension and a belt at the tension
preferred by the wearer.
Method: A total of 31 subjects, screened for previous back
problems and other medical conditions which could be compromised
by lifting, were asked to lift a box of varying weight as if
they were in a manufacturing situation requiring lifting and
lowering 26 to 30 pounds for an eight-hour shift. Subjects adjusted
their flexible elastic support to the tension they preferred.
This was marked and a load cell attached to set the tension to
the same place each time. Lifts were with the belt at this setting,
with the belt at minimal tension and without a belt.
Conclusions: The preferred tension in two different groups
of subjects agreed very closely with a mean tension of 14 to
15 pounds. Also, subjects lifting with a belt at the tension
they preferred were able to lift 13 to 18 percent more than when
they lifted with a belt at minimal tension or without a support.
The study also showed subjects lifting under the same conditions
tended to select a common support tension. For example, those
in a group lifting from knuckle to shoulder height preferred
a higher tension than those lifting from the floor to knuckle
height, perhaps because they did not have to bend as much and
therefore the support was more comfortable.
The authors suggest that maintaining the preferred tension
throughout the day and with regard to the range of the lift may
be an important issue in the reporting of back belt effectiveness.
"Subjects wearing a flexible back support adjusted
to the tension they preferred were able to lift more than those
wearing a belt at minimal tension or without a belt."
David J. Bowen, MS
Published in Advances in Industrial Ergonomics and Safety
VII, proceedings of the 10th annual International Industrial
Ergonomics and Safety Conference, June 1995. (Review by Chase
Ergonomics, Inc. approved by David Bowen, October 1996.)
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