Dynamics of wrist and forearm rotations

We found that (1) the dynamics of movements combining the wrist and forearm are similar to wrist rotations in that stiffness dominates over inertial and damping effects (p<0.0001) by approximately an order of magnitude, (2) the DOF of the wrist and forearm are significantly coupled through stiffness, while interactions due to inertia and damping are small, and (3) despite the complexity of the exact equations of motion, the dynamics of wrist and forearm rotations are well approximated by a simple, linear (but still coupled) model (the mean error in predicting torque was less than 1% of the maximum torque). The exact and approximate models are presented for modeling wrist and forearm rotations in future studies.