Civil Engineering Reference
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FIGURE 48.7 Main screen from the University of Michigan 3D Static Strength Prediction Program for personal
computers shown lifting a 44-lb stock reel. (With permission, Regents of the University of Michigan.)
performed each one. Comparison of the strength prediction programwith the group strength data revealed
a very high correlation (r
0.92) for sagittal plane symmetric exertions. This same study also included
asymmetric simulations with the strength prediction program of 72 different one-arm exertions performed
by five male Army personnel. The correlations ranged from r
¼
0.83. Unfortunately, in this
latter comparison, exact postural and bracing conditions were not available to use in the simulations.
This may have contributed to the lower correlations.
The last validation involved simulations of 56 one- and two-handed, whole-body exertions in 14
different symmetric, bent, and twisted-torso postures (Chaffin and Erig, 1991). The simulation results
were compared with the group strengths of 29 young males. Photographs from several views were avail-
able to assist in replicating the postures used by these subjects. The results indicated that if care is taken to
assure that the posture used in the model simulation is the same as that chosen by people performing the
exertions, the prediction error standard deviation will be less than 6%.
In conclusion, it appears that the strength prediction models and population norms used in the
present models are accurate in predicting the percent of the population capable of performing a large
variety of different types of maximal static exertions. One caution should be noted, however. At
present the strength norms used as limits in the models are based on male and female populations
who are relatively young (i.e., 18-49 yr). To improve the models further, strength values are currently
being gathered on older populations by these investigators. In this regard, one comparison involving
98 men and women with a mean age of 73 yr, showed a major decrease in strength performance in
certain muscle functions. When these decreases were included in the 3DSSPP population data base, it
was found that some exertions that could easily be performed by younger people were predicted to be
impossible to perform by most older people (Chaffin et al., 1994).
0.71 to r
¼
¼
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