On the power spectrum of motor unit action potential trains synchronized with mechanical vibration

Maria Romano, Antonio Fratini, Gaetano D. Gargiulo, Mario Cesarelli, Luigi Iuppariello, Paolo Bifulco

Research output: Contribution to journalArticlepeer-review


Objective: Provide a definitive analysis of the
spectrum of a motor unit action potential train elicited by
mechanical vibratory stimulation via a detailed and concise
mathematical formulation. Experimental studies demonstrated
that motor unit action potentials are not exactly synchronized with the vibratory stimulus but show a variable latency jitter, whose effects have not been investigated yet.

Methods: Synchronized action potential train was represented as a quasi-periodic sequence of a given motor unit waveform. The latency jitter of action potentials was modeled as a Gaussian stochastic process, in accordance to previous experimental studies.

Results: A mathematical expression for power spectrum of a synchronized motor unit action potential train has been derived. The spectrum comprises a significant continuous component and discrete components at the vibratory frequency and its harmonics. Their relevance is correlated to the level of synchronization: the weaker the synchronization, the more relevant the continuous spectrum. EMG rectification enhances the discrete components. Conclusion: The derived equations have general validity and well describe the power spectrum of actual EMG recordings during vibratory stimulation. Results are obtained by appropriately setting the level of synchronization and vibration frequency.

Significance: This study definitively clarifies the nature of changes
in spectrum of raw EMG recordings from muscles undergoing
vibratory stimulation. Results confirm the need of motion artifact
filtering for raw EMG recordings during stimulation and strongly
suggests to avoid EMG rectification that significantly alters the
spectrum characteristics.
Original languageEnglish
Pages (from-to)646 - 653
Number of pages8
JournalIEEE Transactions on Neural Systems and Rehabilitation Engineering
Issue number3
Early online date6 Feb 2018
Publication statusPublished - 6 Mar 2018

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  • EMG spectrum
  • motion artifact
  • motor unit action potential train
  • whole body vibration


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