Identification of a wrist movement model

Tests were performed to find the mechanical properties of the hand and the muscles driving wrist flexion and extension, and the parameters of a model were identified. The hand acts as a pure inertial load over most of its range of motion. The viscosity of the wrist joint is negligible. Passive elastic torques were also small except at extreme wrist angles. Maximum torque is a weak function of angle over a broad range. Torque/velocity curves for muscles were well approximated by a Hill equation. To measure the series elasticity of the muscle equivalents, step changes in torque were imposed. The series stiffness was found to be a monotonically increasing function of the preload, or active state, saturating at high preloads