  Biomechanical motion simulation and dynamic analysis of human joint moments
will provide insights into Musculoskeletal Disorders. As one of the mainstream
simulation tools, OpenSim uses proportional scaling to specify model segment
masses to the simulated subject, which may bring about errors. This study aims
at estimating the errors caused by the specifying method used in OpenSim as
well as the influence of these errors on dynamic analysis. A 3D scan is used to
construct subject's 3D geometric model, according to which segment masses are
determined. The determined segment masses data is taken as the yardstick to
assess the errors of OpenSim scaled model. Then influence of these errors on
the dynamic calculation is evaluated in the simulation of a motion in which the
subject walks in an ordinary gait. Result shows that the mass error in one
segment can be as large as 5.31\% of overall body weight. The mean influence on
calculated joint moment varies from 0.68\% to 12.68\% in 18 joints. In
conclusion, a careful specification of segment masses will increase the
accuracy of the dynamic simulation. As far as estimating human segment masses,
the use of segment volume and density data can be an economical choice apart
from referring to population mass distribution data.
