Phenomenological Modelling of the Nonlinear Flexion–Extension Movement of Human Lower Limb Joints

In this paper we obtain a mathematical model for the flexion–extension (flex-ext) motion of the human lower limb joints in the sagittal plane. This model is composed of a system of differential equations based on quadratic polinoms, obtained from the experimental data collected during walking. Numerical integrations of the mathematical model and the construction of the state space by utilizing numerical solutions and the comparison with the state space obtained from experimental data are obtained. The trajectories of the solution of the phenomenological model are very close to the result of the measurements of the flex-ext angles of the Subject’s joints before the pre-processing stage, but they are narrower, more similar with those obtained after pre-processing.