Civil Engineering Reference
In-Depth Information
48
Static Biomechanical
Modeling in Manual
Lifting
48.1
Introduction ............................
48-1
48.2 Development of Static Strength
Prediction Programs
. .....................
48-2
48.3 Computerization of Strength Prediction and
Back Force Prediction Models
. . .............
48-6
Don B. Chaffin
Charles B. Woolley
University of Michigan
48.4 Validation of Strength and Back Force
Prediction Models
. . . .....................
48-8
48.5
Final Comments ......................... 48-11
48.1 Introduction
Though most manual tasks in industry involve significant body motions, it continues to be very helpful
to evaluate specific exertions within a manual task by performing a static biomechanical analysis. Such
analyses are normally performed by combining the postural information (body angles) obtained from a
stopped frame video image (or photograph) of a worker, and measured forces exerted at the hands. The
latter is often obtained with a simple handheld force gauge.
What follows is a description of a computerized static biomechanical model that has been developed
and used over the last 30 yr to predict:
1. The percentage of men and women who would be capable of exerting specified hand forces in
various work postures
2. The forces acting on various spinal motion segments
Since these two different output predictions have specific criterion values referenced in the NIOSH
Work Practices Guide (NIOSH, 1981), they are often used by professional ergonomists to determine
the relative risk of injury associated with the performance of a manual exertion of interest (Chaffin,
1988a). It also should be noted that the prediction of the percent of the population capable of performing
a specific exertion required on a job is often crucial to the determination of a job specific strength test
score for pre-employment and return to work purposes (Chaffin, 1996). Finally, because the biomechanical
population strengths and low back stresses are predicted by a computerized model which runs on
common personal computer platforms, this has meant that job and product designers and engineers
have been able to simulate various expected high exertion tasks during the early part of the design process,
and thus avoid costly prototype evaluations and retrofits when the products and processes become
operational (Chaffin, 2001). It is this latter application of the biomechanical static strength prediction
48-1
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