Simulation of fatigue related changes in spectral parameters of surface EMG

During fatiguing contractions the power spectrum of surface EMG recordings shows a shift to lower frequencies. Possible causes of this shift are studied with a simulation model. Simulation shows that the shape and the duration of the motor-unit action potential (MUAP) and synchronicity of the firing of motor units influence the median frequency of the power spectrum. It is also shown that the magnitude of this latter effect depends on the proportion of motor units that exhibit synchronicity and the dispersion in their firing moments.<>