Nonlinear Dynamic Analysis of Human Sit-to-Stand Movement with Application to the Robotic Structures

The purpose of this study was to estimate Lyapunov exponents (LE) in order to quantify the local dynamic stability of the lower limb joints during sit-to-stand movement. The values of the Lyapunov exponents are obtained based on the experimental time series of the flexion-extension movements in sagittal plane and the rotational movements in frontal plane for all six main joints of both lower limbs, collected from a sample of healthy subjects and a sample of patients suffering by knee osteoarthritis before total knee replacement. The values of LEs obtained for the osteoarthritic lower limb are associated with more divergence and less stability, being generally, larger than those obtained for the other patient’ limb, and larger than those of healthy joints.