Analysis of human wrist joint impedance: Does human joint viscosity depend on its angular velocity?

A novel model for the mechanical joint impedance, which takes into account the force-velocity relationships of skeletal muscles, is proposed. First, velocity-dependent viscosity changes are formulated using the equation proposed by A. V. Hill. Then, human wrist joint impedance is estimated by a conventional model (a linear model) and the proposed novel model (a nonlinear model) for comparison. The estimated moment of inertia indicates approximately constant value in all muscle contraction levels, and the joint stiffness estimated from the both models increases with the increment of muscle contractions. However, when joint angular velocity starts to change, the estimated joint viscosity dramatically decreases with the increment of joint angular velocity