Elbow Torque Estimated using a Nonlinear Observer

An inverse dynamics model has been designed, using control theory, to estimate elbow joint torque per unit moment of inertia based on a measured movement trajectory. The physiological parameters required by the model (undamped natural frequency and damping ratio of the elbow joint) were measured experimentally using the pendulum test at the elbow joint. Eight subjects participated in the experimental study, which included ten iterations of the standard pendulum test at the elbow joint, as well as ten iterations of the pendulum test with an additional known weight strapped to the wrist. Electrogoniometry was used to record the movement of the forearm during the tests, and surface electromyography of the elbow flexor and extensor muscles was used to ensure that the movements were purely passive. An equation was then derived to calculate the moment of inertia of the forearm as it rotated about the elbow joint. The inverse dynamics model developed in this study could be a useful tool for clinicians in analysing kinematics in patients with neuromuscular or orthopaedic disease.