Civil Engineering Reference
In-Depth Information
35.4 Three-Dimensional Static Strength Prediction
Program Model
The Three-Dimensional Static Strength Prediction Program (3DSSPP) model developed by researchers at
the University of Michigan is a biomechanical modeling system that can be used to compute the
moments
on the joints comprising the kinematic chain. The inputs to this model
are the major joint angles and the direction and magnitude of the force exerted by the hands. Once
this three-dimensional biomechanical model is developed, the three-dimensional moments about the
L5
/
forces acting about
/
S1 joint and spine compression can be calculated (Figure 35.2). Further, the three-dimensional
moments can be compared with the data from the human strength capacity database so that an esti-
mation of the percentage of a population capable of exerting these moments can be generated. Therefore,
two of the measures relevant to the understanding of low back injury risk that can be derived from this
modeling approach are the compression in the spine and the percent of the population that have the
strength capacity to exert the required moments about the spine.
Several studies have illustrated the importance of documenting the relationship between a person's
strength capacity and the physical demands placed on them during work (Chaffin and Park, 1973;
Chaffin, 1974). Chaffin (1974) illustrated a sharp increase in low back pain incidence rates when the
job demands required forces exceeding the workers' strength capacity. This author showed that jobs
whose average lifting strength ratio (LSR — defined as the ratio of the heaviest weight lifted to the
average strength of people asked to perform that lift) exceeded 1.0 had a job related low back incidence
rate (low back incidences
/
0.65 for jobs
whose average LSR was between 0-0.5 and 0.5-1 respectively. Chaffin and Park (1973) performed a very
1000 man-weeks) of
2.3. This is as compared to
0.75 and
/
FIGURE 35.2 A three-dimensional model using the 3DSSPP. (Provided by the Center for Ergonomics, University of
Michigan.)
Search WWH ::
Custom Search