Peripheral and central contributions to evoked contractions during neuromuscular electrical stimulation

• n/a

• Author / Creator

  Bergquist, Austin J

• The present thesis examined two general questions regarding neuromuscular electrical stimulation (NMES): 1) How can the delivery of NMES be optimised to enhance synaptic motor unit recruitment via reflex pathways (central pathways) and 2) Can motor unit recruitment through central pathways improve the fatigue-resistance of NMES-evoked contractions in people with chronic motor-complete spinal cord injury (SCI)?
  To address the first general question, two sets of experiments were conducted with people who were neurologically-intact (Chapters 2 and 3). Information about how motor units were recruited was provided by electromyographic responses evoked during NMES. The first two sets of experiments tested the hypothesis that NMES delivered over the nerve trunk (nNMES) would generate contractions of the plantar flexors (Chapter 2) and knee extensors (Chapter 3) with greater activity through central pathways compared with contractions of equivalent amplitude evoked by NMES delivered over the muscle belly (mNMES). Both hypotheses were confirmed, indicating that nNMES may hold significant advantages over mNMES for rehabilitation, and in particular for generating fatigue-resistant contractions.
  To address the second general question, two sets of experiments were conducted in people with chronic motor-complete SCI (Chapters 4 and 5). The first set of experiments tested whether contractions of the paralysed plantar flexors evoked by mNMES would fatigue sooner, and to a greater extent, compared with contractions of equivalent amplitude generated by nNMES. This hypothesis was confirmed. However, differences in fatigue-resistance between NMES sites were dependent upon the contribution of central pathways (H-reflexes) during the evoked contractions. When contractions were generated only through successive motor axon activation (M-waves; peripheral pathways), NMES site had no influence on fatigue-resistance. The second set of experiments tested the hypothesis that contractions of the paralysed plantar flexors evoked by nNMES using a short pulse duration (50 µs) would fatigue sooner, and to a greater extent, compared with contractions of equivalent amplitude evoked by nNMES using a long pulse duration (1000 µs). Data collection for this project continues, however initial data support our hypothesis. In conclusion, activity through central pathways is dependent upon NMES site, and holds promise for generating fatigue-resistant contractions after SCI.

• Subjects / Keywords

  • Recruitment
  • Fatigue
  • Motor unit
  • Spinal cord injury
  • H-reflex
  • M-wave

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R34Q7R17X

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.