Simulift: a simulation model of human trunk motion

In this paper, the authors present a deterministic simulation model, which they call Simulift, of trunk-muscle activity and intra-abdominal pressure during a sagittally symmetric trunk exertion. Simulift is a descriptive model that quantifies the time-varying loading of the spine based on observed internal forces. Recent findings about the time sequence of events during trunk motion and established equilibrium formulas provide the theoretical bases for the simulation. A profile of electromyographic activity in ten trunk muscles and intra-abdominal pressure is updated as simulated time passes, or as the trunk motion is simulated. Input to the model includes a list of motion-event times and a set of profile-component-behavior data. Simulift is an "impulse" model that computes instantaneous and time-integrated statistics on individual muscle activity, intra-abdominal pressure, compression, lateral shear, and anterior shear as the profile components of the simulated subject change. Computer results for the simulation model are presented.