The Myoelectric Signal of Electrically Stimulated Muscle During Recruitment: An Inherent Feedback Pareter for a Closed-Loop Control Scheme

The myoelectric profile of an electrically stimulated muscle with separate and simultaneous control of firing rate and recruitment was determined. The signal consists of low amplitude, desynchronous discharge at low recruitment levels and exhibits monotonic, distinct compound action potentials at moderate to full recruitment. The myoelectric signal-force model is described by sigmoidal function when the signal is represented by its median frequency (MF), rms, or mean absolute value (MAV) at firing rates inducing just above fused force response (~28 pps). At firing rates corresponding to the maximal tetanic force of the muscle (~51 pps) the MES-force model is represented by a second-order polynomial for MF, rms, and MAV. Dynamic tracking of force induced by a sinusoidal recruitment/derecruitment of the muscle´s motor unit pool at frequencies in the range of 0-1 Hz show that the MAV is independent, whereas the rms and MF are dependent on tracking frequency. The linearized MAV-force model was found superior for use as a sensorless force feedback measurement in a closed-loop control scheme aimed at restoration of regulated movement to a paralyzed limb joint.