The proposed dynamic optimization framework aimed to solve spine kinematics based on 3D skin-marker positions while simultaneously calibrating spine stiffness. Previously used methods and models for solving spine kinematics are commonly static-based and are constrained with strict kinematics bounds. Our proposed optimization approach enforces dynamic consistency in the entire skeletal system and over the entire time-trajectories, as well as the subject-specific nonlinear properties of joint stiffness. Thereby the approach prevents unrealistic joint motions and kinematic inconsistencies caused by uncertainties in body segment parameters and experimental measurement errors.

More details can be found here:
https://link.springer.com/article/10.1007/s10439-021-02774-3