Motor unit firing behavior in slow and fast contractions of the first dorsal interosseous muscle of healthy men

Yoshihisa Masakado, Kazuto Akaboshi, Masa aki Nagata, Akio Kimura, Naoichi Chino

Research output: Contribution to journalArticlepeer-review

60 Citations (Scopus)


The motor unit recruitment threshold and firing rate were evaluated during slow and fast contraction of the first dorsal interosseous (FDI) muscle by healthy young men. Using a special quadrifilar electrode myoelectric activity was recorded during voluntary isometric contraction. Motor unit action potentials (MUAPs) were decomposed into individual MUAP trains by the electromyography (EMG) signal decomposition technique. Recruitment thresholds of the motor units decreased with the increase in the speed of contraction, and there was no recruitment reversal despite the increase. In terms of rate coding, the firing rates of the motor units increased as the speed of contraction increased; however, a high threshold motor unit always had a lower firing rate than a low threshold motor unit regardless of the contraction speed. At all contraction speeds, recruitment and rate coding may act through the same mechanism. If excitation of the motoneuron pool occurs rather than excitation of an individual motoneuron, a low threshold motor unit is easier to recruit and fire repetitively than a high threshold one. The motor unit firing behavior during fast contraction basically may be the same as during slow contraction.

Original languageEnglish
Pages (from-to)290-295
Number of pages6
JournalElectroencephalography and Clinical Neurophysiology/ Electromyography
Issue number6
Publication statusPublished - 1995 Dec


  • Decomposition technique
  • Fast contraction
  • Firing rate
  • Motor unit
  • Recruitment threshold
  • Size principle

ASJC Scopus subject areas

  • Neuroscience(all)
  • Clinical Neurology


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