Perturbation-based measurement of real and imaginary parts of human arm´s mechanical impedance

Mechanical impedance is a complex number and a system´s property. Impedance of human arm is the control variable when the central nervous system coordinates a motion. This research proposes a new method for measuring the mechanical impedance as a complex number. Impedance is measured at the hand point while sinusoidal perturbation is applied. That helps extracting the real and imaginary part of the impedance. Simulations reveal how spring, mass, and damper contribute to the mechanical impedance. Despite the simulation results, our experiment shows that damping which is the real part of impedance is not frequency independent and imaginary part of mechanical impedance decreased with increasing frequency that in turn suggests the stiffness is increasing.