Multi-body musculoskeletal dynamic model of the human trunk based on an experimental approach

To overcome certain back pain problems or enhance body performance in sports applications, a biomechanical study of the dynamic response of the human trunk is important to understand and predict its response in different loading conditions involving time-dependent excitations. In this work, it is proposed to use a simple experimental protocol and a 3D finite element dynamic model to extract effective stiffness, inertial and damping characteristics of the human trunk. A setup is designed to collect data from the motion of the trunk of a healthy subject attached around its pelvis, in an upright position with a small time-dependent applied force to its thoracic region via a securely designed small-amplitude crank-rod mechanism. The applied force and the subsequent displacements at the thoracic vertebrae T8 level are measured using a load cell and a laser displacement sensor, respectively. The experimental results are used to update a 3D multi-body musculoskeletal model. The model of the trunk is subdivided into 335 elements with independent geometrical and physical properties. A Newmark method is used to solve the derived equations in time, extract the dynamic properties of the trunk, and compare the results with those obtained experimentally. It is also shown that the simulated transient displacement is similar to the one obtained experimentally for relatively small time intervals. The collected experimental data are used to calculate the effective mass, stiffness, and damping factor and observe the effect of the applied excitation conditions on the dynamic response. These results are compared with those obtained numerically with the developed musculoskeletal model. Good agreement was observed for the variation of the effective dynamic properties of the trunk between the experimental and numerical results.