The estimation of motor unit twitch tensions in the human masseter muscle by spike‐triggered averaging

A. S. McMillan, K. Sasaki, A. G. Hannam

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


Spike‐triggered averaging (STA) has been used to extract twitch profiles of single motor units (SMU) within the human masseter muscle. However, the reported twitch tensions may have been biased by thevoluntary firing frequency of the SMUs, the complex architecture ofthe muscle, and by the biomechanical linkage of the jaw. In this study, a rigid STA paradigm was used to record spike‐triggered “measured tensions” (STMTs) for 32 SMUs in the masseter musclesof four subjects. STMTs were recorded at two different orientations of a force transducer placed between the incisor teeth. The STMTs produced by each unit were used to calculate jaw torque. STMTs were also recorded in 11 units with differing degrees of muscle coactivation. STMTs for each unit varied according to the orientation of the force transducer. However, no systematic changes in STMTs occurred with reciprocal changes in the jaw moment arm. STMTs could be altered significantly by different degrees of muscle co‐activation. The use of STA as a method for determining SMU tension in the human masseter muscle appears to be highly task‐dependent and in the presence of co‐activation may be inappropriate.

Original languageEnglish
Pages (from-to)697-703
Number of pages7
JournalMuscle & Nerve
Issue number8
Publication statusPublished - 1990 Aug
Externally publishedYes


  • masseter
  • single motor units
  • spike‐triggered averaging
  • twitch tension

ASJC Scopus subject areas

  • Physiology
  • Clinical Neurology
  • Cellular and Molecular Neuroscience
  • Physiology (medical)


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