Motor unit activation order during electrically evoked contractions of paralyzed or partially paralyzed muscles

Christine K. Thomas, Gary Nelson, Lara Than, Inge Zijdewind

Research output: Contribution to journalArticle

59 Scopus citations

Abstract

The activation order of motor units during electrically evoked contractions of paralyzed or partially paralyzed thenar muscles was determined in seven subjects with chronic cervical spinal cord injury. The median nerve was stimulated percutaneously with pulses of graded intensity to produce increments in the compound electromyogram (EMG) and force. Each increment corresponded to the activation of another unit. The evoked unit EMG and force was obtained by digital subtraction. The thenar muscles had between 15 and 83 units (26 ± 19) that produced 114.3 ± 127.1 mN force (n = 290). In six subjects, a significant positive correlation was found between activation order and unit force indicating that weaker units were excited before stronger units. These data are contrary to the notion that a reversal of unit activation order occurs during evoked versus voluntary contractions.

Original languageEnglish (US)
Pages (from-to)797-804
Number of pages8
JournalMuscle and Nerve
Volume25
Issue number6
DOIs
StatePublished - 2002

Keywords

  • Electrical stimulation
  • Motor unit recruitment
  • Muscle fatigue
  • Muscle paralysis
  • Spinal cord injury

ASJC Scopus subject areas

  • Clinical Neurology
  • Neuroscience(all)

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