Effects of sustained stimulation on the excitability of motoneurons innervating paralyzed and control muscles

Jane E. Butler, Christine K. Thomas

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


The excitability of thenar motoneurons (reflected by F-wave persistence and amplitude) and thenar muscle force were measured during a stimulation protocol (90 s of 18-Hz supramaximal electrical stimulation of the median nerve) designed to induce muscle fatigue (force decline). Data from muscles (n = 15) paralyzed by chronic cervical spinal cord injury were compared with those obtained from control muscles (n = 6). The persistence of F waves in both paralyzed and control muscles increased from ∼60 to ∼76% during the first 10 s of the fatigue protocol. Persistence then declined progressively to ∼33% at 90 s. These changes in F-wave persistence suggest that similar reductions occur in the excitability of the motoneurons to paralyzed and control motor units after sustained antidromic activation. Despite this, significantly larger force declines occurred in the paralyzed muscles of spinal cord-injured subjects (∼60%) than in the muscles of control subjects (∼15%). These data suggest that the decreases in motoneuron excitability for both the spinal cord-injured and control subjects are a result of activity-dependent changes in motoneuron properties that are independent of fatigue-related processes in the muscles.

Original languageEnglish (US)
Pages (from-to)567-575
Number of pages9
JournalJournal of applied physiology
Issue number2
StatePublished - Feb 1 2003


  • Electrical stimulation
  • F-wave persistence
  • Motoneuron excitability
  • Paralyzed muscle
  • Spinal cord injury

ASJC Scopus subject areas

  • Physiology
  • Endocrinology
  • Orthopedics and Sports Medicine
  • Physical Therapy, Sports Therapy and Rehabilitation


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