Contraction fatigue and motor unit overlap in the tibialis anterior during different intensities of interleaved electrical stimulation

• Author / Creator

  Ainsley, Emily N.

• Interleaved neuromuscular electrical stimulation (iNMES), which involves alternating stimulus pulses between a nerve (nNMES) and muscle belly (mNMES), has been demonstrated to reduce fatigue of the ankle dorsiflexors when used with relatively low contraction amplitudes. However, the amount of fatigue accrued at higher intensities of NMES has not been investigated, when theoretically higher overlap between the motor units (MUs) recruited with stimulation at each site may reduce its effectiveness. The present experiments were designed to determine the effect of contraction amplitude on the amount of fatigue and MU overlap in the tibialis anterior muscle. Fourteen participants completed 3 testing sessions on 3 separate days during which fatigue protocols of iNMES were delivered over the common peroneal nerve and tibialis anterior muscle belly at one of (LOW: ~5% MVC, MID: ~15% MVC, MAX: the greatest tolerable stimulation amplitude; ~30% MVC) were administered. Each fatigue protocol consisted of 180 iNMES-evoked contractions (40 Hz; 500µs; 0.3 s “on", 0.7 s “off”). Fatigue was quantified as the percent decline in torque from beginning to the end of the fatigue protocol. MU overlap (%) was quantified by comparing the amount of torque produced at each stimulation site separately to that produced when stimulation was delivered over both sites at the same time. Contraction fatigue was found to be not different across the three contraction amplitudes. MU overlap was higher during MAX than during LOW and was found to have a significant positive correlation with contraction amplitude. However, no significant relationship was found between MU overlap and contraction fatigue. These data suggest that across a moderate range of contraction amplitudes, contraction fatigue remains consistent during iNMES and does appear to be influenced by the amount of overlap in MUs recruited by each stimulation site.

• Subjects / Keywords

  • Contraction fatigue
  • Motor unit overlap
  • Neuromuscular electrical stimulation

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R32N5000X

• 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.