Motor unit power spectrum and firing rate

Changes in the power density spectrum of myoelectric signal with contraction level have been reported in the literature. These changes can be induced by a number of possible factors including recruitment of differing types of units, conduction velocity changes and firing rate changes. In the paper the single unit power spectrum is investigated and the effects of firing rate mean and variance changes evaluated. Motor unit signal simulation and experiments are carried out to verify predictions. The results show that spectrum peaks will shift with firing rate and the median frequency is weakly dependent on firing rate.