title: Depression and recovery of reflex amplitude during electrical stimulation after spinal cord injury.
abstract: OBJECTIVE
  The aim of this study was to quantify, for the first time, H-reflexes evoked during prolonged trains of wide-pulse neuromuscular electrical stimulation (WP-NMES) in individuals with chronic spinal cord injury (SCI). We hypothesised that after the first H-reflex, reflex amplitudes would be depressed (due to post-activation depression), but would recover and this recovery would be enhanced after a "burst" of 100 Hz WP-NMES.
  
  
  METHODS
  Soleus M-waves and H-reflexes evoked during WP-NMES (1 ms pulse width) of the tibial nerve were quantified in nine individuals with SCI. WP-NMES was delivered in two patterns: "constant-frequency" (15 or 20 Hz for 12 s) and "burst-like" (15-100-15 Hz or 20-100-20 Hz; 4 s each phase) at an intensity that evoked an M-wave between 10% and 15% of the maximal M-wave (M(max)).
  
  
  RESULTS
  During constant frequency stimulation, after the initial depression from the first to the second H-reflex (1st: 57% M(max); 2nd: 25% M(max)), H-reflexes did not recover significantly and were 37% M(max) at the end of the stimulus train. During the burst-like pattern, after the initial depression (1st: 62% M(max); 2nd: 30%), reflexes recovered completely by the end of the stimulation (to 55% M(max)) as they were not significantly different from the first H-reflex. M-waves were initially depressed (1st: 12% M(max); 2nd: 7% M(max)) then did not change throughout the stimulation and were not significantly different between stimulation patterns. An analysis of covariance indicated that the depression in M-wave amplitude did not account for the depression in H-reflex amplitude.
  
  
  CONCLUSIONS
  Relatively large H-reflexes were recorded during both patterns of NMES. The brief burst of 100 Hz stimulation restored H-reflexes to their initial amplitudes, effectively reversing the effects of post-activation depression.
  
  
  CONCLUSIONS
  For individuals with chronic SCI, generating contractions through central pathways may help reduce muscle atrophy and produce contractions that are more fatigue-resistant for rehabilitation, exercise programs, or to perform activities of daily living.
authors.affiliation: Centre for Neuroscience, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: J M
authors.initials: JM
authors.lastname: Clair-Auger
authors.forename: O
authors.initials: O
authors.lastname: Lagerquist
authors.forename: D F
authors.initials: DF
authors.lastname: Collins
mesh_terms: D000293:Adolescent; D000328:Adult; D001369:Axons / Q000502:physiology; D003627:Data Interpretation, Statistical; D004558:Electric Stimulation; D004576:Electromyography; D055724:Electrophysiological Phenomena / Q000502:physiology; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D020127:Recovery of Function / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000502:physiology; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D013979:Tibial Nerve / Q000502:physiology; D058067:Wavelet Analysis; D055815:Young Adult