title: H-reflexes reduce fatigue of evoked contractions after spinal cord injury.
abstract: BACKGROUND
  Neuromuscular electrical stimulation (NMES) over a muscle belly (mNMES) generates contractions predominantly through M-waves, while NMES over a nerve trunk (nNMES) can generate contractions through H-reflexes in people who are neurologically intact. We tested whether the differences between mNMES and nNMES are present in people with chronic motor-complete spinal cord injury and, if so, whether they influence contraction fatigue.
  
  
  METHODS
  Plantar-flexion torque and soleus electromyography were recorded from 8 participants. Fatigue protocols were delivered using mNMES and nNMES on separate days.
  
  
  RESULTS
  nNMES generated contractions that fatigued less than mNMES. Torque decreased the least when nNMES generated contractions, at least partly through H-reflexes (n = 4 participants; 39% decrease), and torque decreased the most when contractions were generated through M-waves, regardless of NMES site (nNMES 71% decrease, n = 4; mNMES, 73% decrease, n = 8).
  
  
  CONCLUSIONS
  nNMES generates contractions that fatigue less than mNMES, but only when H-reflexes contribute to the evoked contractions.
authors.affiliation: Faculty of Physical Education and Recreation, E-488 Van Vliet Centre, University of Alberta, Edmonton, Alberta, Canada, T6G 2H9; Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Austin J
authors.initials: AJ
authors.lastname: Bergquist
authors.forename: Matheus J
authors.initials: MJ
authors.lastname: Wiest
authors.forename: Yoshino
authors.initials: Y
authors.lastname: Okuma
authors.forename: David F
authors.initials: DF
authors.lastname: Collins
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005221:Fatigue / Q000209:etiology*; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D011999:Recruitment, Neurophysiological / Q000502:physiology; D013119:Spinal Cord Injuries / Q000150:complications* / Q000473:pathology*; D019415:Torque
keywords: M-wave; electrical stimulation; motor unit; recruitment; size principle