Modeling of surface myoelectric signals - Part I: Model implementation

The relationships between the parameters of active motor units (MU's) and t he features of surface electromyography (EMG) signals have been investigate d using a mathematical model that represents the surface EMG as a summation of contributions from the single muscle fibers. Each MU has parallel fiber s uniformly scattered within a cylindrical volume of specified radius embed ded in an anisotropic medium. Two action potentials, each modeled as a curr ent tripole, are generated at the neuromuscular junction, propagate in oppo site directions and extinguish at the fiber-tendon endings, The neuromuscul ar junctions and fiber-tendon endings are uniformly scattered within region s of specified width, Muscle fiber conduction velocity and average fiber le ngth to the right and left of the center of the innervation zone are also s pecified. The signal produced by MU's with different geometries and conduct ion velocities are superimposed. Monopolar, single differential and double differential signals are computed from electrodes placed in equally spaced locations on the surface of the muscle and are displayed as functions of an y of the model's parameters. Spectral and amplitude variable's and conducti on velocity are estimated from the surface signals and displayed as functio ns of any of the model's parameters. The influence of fiber-end effects, el ectrode misalignment, tissue anisotropy, MU's location and geometry are dis cussed. Part II of this paper will focus on the simulation and interpretati on of experimental signals.