Fig. 1.

Model of upper limb neuromusculoskeletal dynamics used to simulate tremor propagation. The excitation-contraction dynamics of muscle low-pass filters muscle activity into muscle force; the musculoskeletal geometry of the limb mixes force from various muscles into joint torques; and the mechanical impedance filters and mixes joint torques, resulting in joint displacement. $t_1$ and $t_2$ are time constants representing the dynamics of muscle excitation and contraction, respectively; $C$ is the gain between muscle activity and muscle force; $M$ is a matrix of moment arms; $I$, $D$, and $K$ are matrices representing the coupled joint inertia, damping, and stiffness, respectively.