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Interleaved Neuromuscular Electrical Stimulation
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- Author / Creator
- Joner Wiest, Matheus
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Neuromuscular electrical stimulation (NMES) is used to produce contractions to restore movement and reduce secondary complications for individuals experiencing paralysis. NMES is traditionally delivered through electrodes over a muscle belly (mNMES) or superficial nerve trunk (nNMES). Unfortunately, both methods are limited by rapid fatigability of the evoked contractions due in part to the non-physiologically high frequencies at which motor units (MUs) discharge. In order to reduce this fatigability, interleaved NMES (iNMES) was developed, which involves alternating stimulus pulses between the mNMES and nNMES sites. iNMES takes advantage of the fact that different MUs can be recruited by each NMES site. Therefore, alternating stimulus pulses reduces the discharge rate of recruited MUs, resulting in less fatigability than during traditional NMES. The experiments described in this thesis were designed to address gaps in knowledge about iNMES to develop a better understanding about how best to use iNMES for rehabilitation. The first project, described in Chapter 2 , was designed to estimate the effect of stimulation amplitude on the overlap between MUs recruited by mNMES, delivered over the tibialis anterior (TA) muscle belly, and nNMES, delivered over the common peroneal nerve. We showed that overlap increased progressively with increases in stimulation amplitude until overlap reached 72%. Further, trains of iNMES delivered at the stimulation amplitude that produced the least overlap (5%) generated contractions of 25% of a maximal voluntary isometric contraction (MVIC). The second project, described in Chapter 3, characterized the effect of stimulation frequency and pathway on torque generated by mNMES, nNMES and iNMES delivered to TA and the triceps surae (TS). In general, iNMES generated more torque at the same “net” frequency as mNMES and nNMES in both muscles. For TA, contractions were generated predominantly by the activation of motor axons, thus through peripheral pathways, independent of NMES type. For the TS, mNMES produced contractions predominantly through peripheral pathways; however, central pathways predominated during nNMES and, to a lesser extent during iNMES. Plantarflexion torque during nNMES reached a steady state at a lower frequency (20 Hz) than mNMES (60 Hz) or iNMES (80 Hz) which was most likely due to frequency-dependent depression of transmission along central pathways. The final project, described in Chapter 4, was designed to compare discomfort when the three types of NMES were delivered to generate submaximal contractions and identify the maximal torque that could be generated by each type of NMES before discomfort became a limiting factor. Results indicate there were no differences in discomfort between NMES types when torque was low (5-20% MVIC). However, during the maximal torque trials, nNMES produced significantly more torque (65% MVIC) than mNMES (33% MVIC) with significantly less discomfort. iNMES generated contractions of 49% MVIC with discomfort that was not different than mNMES or nNMES. Collectively, this series of experiments address gaps in our knowledge about iNMES. Interestingly, iNMES can produce five times the torque required to dorsiflex the ankle during the swing phase of walking when stimulation amplitude and, consequently, overlap were low. iNMES also produced more torque at a given net frequency than traditional NMES. Both of these results bode well for producing contractions of sufficient amplitude to be used for rehabilitation while minimizing fatigability by reducing MU discharge rates. iNMES provided these major advantages with a similar level of discomfort as traditional NMES, offering an overall superior method of NMES delivery than traditional NMES. In conclusion, iNMES reduces MU discharge rates without compromising the capacity to generate functionally relevant torque, making it a potentially valuable new rehabilitative tool after paralysis. Further research is necessary to test if these advantages translate into improved outcomes of NMES-based rehabilitation programs.
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- Graduation date
- Fall 2016
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- 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.