Spectral Analysis of Surface Motor Unit Action Potentials and Surface Interference Electromyogram

Surface interference electromyograms (EMG´s) were recorded from the tibial muscle of a healthy subject during 50 percent maximal contraction and single motor unit action potentials (MUAP´s) were isolated by averaging from the interference pattern. The formation of the EMG was simulated by summing isolated MUAP´s according to the statistical properties of the corresponding motor unit discharges. Power spectral density functions (PSDF´s) were finally computed for single MUAP´s as well as for simulated and experimental EMG´s and compared with each other.