title: Comparison of the ballistic contractile responses generated during microstimulation of single human motor axons with brief irregular and regular stimuli.
abstract: Ballistic contractions are induced by brief, high-frequency (60-100 Hz) trains of action potentials in motor axons. During ramp voluntary contractions, human motoneurons exhibit significant discharge variability of ∼20% and have been shown to be advantageous to the neuromuscular system. We hypothesized that ballistic contractions incorporating discharge variability would generate greater isometric forces than regular trains with zero variability.
  
  
  
  High-impedance tungsten microelectrodes were inserted into human fibular nerve, and single motor axons were stimulated with both irregular and constant-frequency stimuli at mean frequencies ranging from 57.8 to 68.9 Hz.
  
  
  
  Irregular trains generated significantly greater isometric peak forces than regular trains over identical mean frequencies.
  
  
  
  The high forces generated by ballistic contractions are not based solely on high frequencies, but rather a combination of high firing rates and discharge irregularity. It appears that irregular ballistic trains take advantage of the "catchlike property" of muscle, allowing augmentation of force. Muscle Nerve 56: 292-297, 2017.
authors.affiliation: School of Medicine, Western Sydney University, Locked Bag 1797, 183 Narellan Road, Penrith, New South Wales, 2751, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Leitch
authors.affiliation: School of Medicine, Western Sydney University, Locked Bag 1797, 183 Narellan Road, Penrith, New South Wales, 2751, Australia.
authors.forename: Vaughan G
authors.initials: VG
authors.lastname: Macefield
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000293:Adolescent; D000328:Adult; D001369:Axons / Q000502:physiology*; D055592:Biophysical Phenomena / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008839:Microelectrodes; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D055815:Young Adult
keywords: ballistic; discharge variability; force; irregularity; microstimulation; rate coding