A Procedure for Adjustment of Body Segmental Parameter Values to Individual Subjects in Inverse Dynamics

A procedure of inverse dynamics was developed to adjust the body segmental parameter values to individual subjects. Newton's second law was utilized, which states that a resultant force vector (the sum of all forces acting on a rigid body) can be calculated from the mass of the body and the acceleration vector of the center of mass of the body. By comparing the measured resultant force and the calculated resultant force, it was possible to evaluate the errors that exist in body segmental parameter values. These errors were minimized through simulated annealing numerical optimization that searched for the optimal values of body segmental parameters. A three-dimensional neuromusculoskeletal model was used to generate error-free sets of kinematic and kinetic data. Two types of jumping motion, i.e., squat jumping and countermovement jumping, were generated through forward dynamic computer simulation. In the process of analysis, randomly generated errors were introduced into body segmental parameter values, i.e., the mass and the location of the center of mass of each segment. The procedure developed in this study successfully reduced the errors in those body segmental parameter values. The average error for the mass was 0.97% whereas the average error for the location of the center of mass was 6.04%.