Decreased excitability of motor axons contributes substantially to contraction fatigability during neuromuscular electrical stimulation

2020 ◽  
Author(s):  
Minh John Luu ◽  
Kelvin E. Jones ◽  
David F. Collins
Keyword(s):  
Electrical Stimulation ◽  
Time Course ◽  
Tibialis Anterior Muscle ◽  
Neuromuscular Electrical Stimulation ◽  
Motor Units ◽  
Drop Out ◽  
Motor Axon ◽  
Dependent Manner ◽  
Motor Axons ◽  
Axonal Excitability

The present study was designed to: 1) determine the time course of changes in motor axon excitability during and after neuromuscular electrical stimulation (NMES), and 2) characterise the relationship between contraction fatigability, NMES frequency, and changes at the axon, neuromuscular junction, and muscle. Eight neurologically-intact participants attended three sessions. NMES was delivered over the common peroneal nerve at 20, 40, or 60 Hz for 8 min (0.3 s “on”, 0.7 s “off”). Threshold tracking was used to measure changes in axonal excitability. Supramaximal stimuli were used to assess neuromuscular transmission and force-generating capacity of the tibialis anterior muscle. Torque decreased 49 and 62% during 8 min of 40 and 60 Hz NMES, respectively. Maximal twitch torque decreased only during 60 Hz NMES. Motor axon excitability decreased by 14, 27, and 35% during 20, 40, and 60 Hz NMES, respectively. Excitability recovered to baseline immediately (20 Hz), 2 min (40 Hz), and 4 min (60 Hz) following NMES. Overall, decreases in axonal excitability best predicted how torque declined over 8 min of NMES. During NMES, motor axons become less excitable and motor units “drop out” of the contraction, contributing substantially to contraction fatigability and its dependence on NMES frequency. NOVELTY BULLETS • The excitability of motor axons decreased during neuromuscular electrical stimulation (NMES) in a frequency-dependent manner. • As excitability decreased, axons failed to reach threshold and motor units dropped out of the contraction. • Overall, decreased excitability best predicted how torque declined and thus is a key contributor to fatigability during NMES.

scholarly journals Modulation of torque evoked by wide-pulse, high-frequency neuromuscular electrical stimulation and the potential implications for rehabilitation and training

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chris Donnelly ◽  
Jonathan Stegmüller ◽  
Anthony J. Blazevich ◽  
Fabienne Crettaz von Roten ◽  
Bengt Kayser ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
High Frequency ◽  
Neuromuscular Electrical Stimulation ◽  
Motor Units ◽  
Progressive Increase ◽  
Great Promise ◽  
Measured Parameter ◽  
Time Integral ◽  
Spinal Circuitry ◽  
Evoked Force

AbstractThe effectiveness of neuromuscular electrical stimulation (NMES) for rehabilitation is proportional to the evoked torque. The progressive increase in torque (extra torque) that may develop in response to low intensity wide-pulse high-frequency (WPHF) NMES holds great promise for rehabilitation as it overcomes the main limitation of NMES, namely discomfort. WPHF NMES extra torque is thought to result from reflexively recruited motor units at the spinal level. However, whether WPHF NMES evoked force can be modulated is unknown. Therefore, we examined the effect of two interventions known to change the state of spinal circuitry in opposite ways on evoked torque and motor unit recruitment by WPHF NMES. The interventions were high-frequency transcutaneous electrical nerve stimulation (TENS) and anodal transcutaneous spinal direct current stimulation (tsDCS). We show that TENS performed before a bout of WPHF NMES results in lower evoked torque (median change in torque time-integral: − 56%) indicating that WPHF NMES-evoked torque might be modulated. In contrast, the anodal tsDCS protocol used had no effect on any measured parameter. Our results demonstrate that WPHF NMES extra torque can be modulated and although the TENS intervention blunted extra torque production, the finding that central contribution to WPHF NMES-evoked torques can be modulated opens new avenues for designing interventions to enhance WPHF NMES.

scholarly journals Anatomical Consideration of the Motor Point Location of the Tibialis Anterior Muscle for effective Neuromuscular Electrical Stimulation

2011 ◽  
Vol 23 (3) ◽  
pp. 381-384 ◽  
Author(s):  
Hirokazu Narita ◽  
Shoji Chiba ◽  
Hideki Yoshida ◽  
Hideaki Mizohata ◽  
Yoshikazu Tonosaki ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Tibialis Anterior ◽  
Tibialis Anterior Muscle ◽  
Neuromuscular Electrical Stimulation ◽  
Motor Point ◽  
Point Location

Single motor axon conduction velocities of human upper and lower limb motor units. A study with transcranial electrical stimulation

2002 ◽  
Vol 113 (2) ◽  
pp. 284-291 ◽  
Author(s):  
Francesca Dalpozzo ◽  
Pascale Gérard ◽  
Victor De Pasqua ◽  
François Wang ◽  
Alain Maertens de Noordhout
Keyword(s):  
Electrical Stimulation ◽  
Lower Limb ◽  
Motor Units ◽  
Motor Axon ◽  
Transcranial Electrical Stimulation ◽  
Single Motor ◽  
Conduction Velocities

scholarly journals Modulation of motor unit activity in biceps brachii by neuromuscular electrical stimulation applied to the contralateral arm

2015 ◽  
Vol 118 (12) ◽  
pp. 1544-1552 ◽  
Author(s):  
Ioannis G. Amiridis ◽  
Diba Mani ◽  
Awad Almuklass ◽  
Boris Matkowski ◽  
Jeffrey R. Gould ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Motor Unit ◽  
Unit Activity ◽  
Pulse Width ◽  
Biceps Brachii ◽  
Neuromuscular Electrical Stimulation ◽  
Motor Units ◽  
Elbow Flexors ◽  
Discharge Characteristics ◽  
Low Threshold

The purpose of the study was to determine the influence of neuromuscular electrical stimulation (NMES) current intensity and pulse width applied to the right elbow flexors on the discharge characteristics of motor units in the left biceps brachii. Three NMES current intensities were applied for 5 s with either narrow (0.2 ms) or wide (1 ms) stimulus pulses: one at 80% of motor threshold and two that evoked contractions at either ∼10% or ∼20% of maximal voluntary contraction (MVC) force. The discharge times of 28 low-threshold (0.4–21.6% MVC force) and 16 high-threshold (31.7–56.3% MVC force) motor units in the short head of biceps brachii were determined before, during, and after NMES. NMES elicited two main effects: one involved transient deflections in the left-arm force at the onset and offset of NMES and the other consisted of nonuniform modulation of motor unit activity. The force deflections, which were influenced by NMES current intensity and pulse width, were observed only when low-threshold motor units were tracked. NMES did not significantly influence the discharge characteristics of tracked single-threshold motor units. However, a qualitative analysis indicated that there was an increase in the number of unique waveforms detected during and after NMES. The findings indicate that activity of motor units in the left elbow flexors can be modulated by NMES current and pulse width applied to right elbow flexors, but the effects are not distributed uniformly to the involved motor units.

scholarly journals Impact of electrode geometry on force generation during functional electrical stimulation

2015 ◽  
Vol 1 (1) ◽  
pp. 458-461 ◽  
Author(s):  
Jan C. Loitz ◽  
Aljoscha Reinert ◽  
Dietmar Schroeder ◽  
Wolfgang H. Krautschneider
Keyword(s):  
Electrical Stimulation ◽  
Functional Electrical Stimulation ◽  
Spatial Orientation ◽  
The Other ◽  
Motor Axon ◽  
Force Generation ◽  
Electrode Placement ◽  
Electrode Geometry ◽  
Motor Axons ◽  
Force Measurements

AbstractThe goal of functional electrical stimulation is to restore lost movements by excitation of motor axons inner-vating the target muscle. For optimal electrode placement and geometry the distribution and spatial orientation of the desired motor axons has to be known. In this study, the response of motor axons with different orientations to electrical stimulation was simulated. Three electrode geometries with the same area were used. The simulated axon activation was compared to experimental force measurements and showed good agreements. It is now assumed that optimal electrode geometry does strongly depend on motor axon orientation, which can vary from one subject to the other. Lack of knowledge about the dominant motor axon orientation makes the use of square, round or multi-pad electrodes favorable.

Does increasing the number of channels during neuromuscular electrical stimulation reduce fatigability and produce larger contractions with less discomfort?

2021 ◽  
Author(s):  
Trevor Scott Barss ◽  
Bailey WM Sallis ◽  
Dylan J Miller ◽  
David F Collins
Keyword(s):  
Electrical Stimulation ◽  
High Current Density ◽  
Neuromuscular Electrical Stimulation ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Secondary Outcome ◽  
High Current ◽  
Firing Rates ◽  
Multiple Electrodes ◽  
Neurologically Intact

Abstract Purpose: Neuromuscular electrical stimulation (NMES) recruits motor units (MUs) at unphysiologically high rates, leading to contraction fatigability. Rotating NMES pulses between multiple electrodes recruits different MUs from each site, reducing MU firing rates and fatigability. This study aimed to determine whether rotating pulses between an increasing number of stimulation channels (cathodes) reduces contraction fatigability and increases the ability to generate torque during NMES. A secondary outcome was perceived discomfort. Methods: Fifteen neurologically-intact volunteers completed 4 sessions. NMES was delivered over the quadriceps through 1 (NMES1), 2 (NMES2), 4 (NMES4) or 8 (NMES8) channels. Fatigability was assessed over 100 contractions (1s on/1s off) at an initial contraction amplitude that was 20% of a maximal voluntary contraction (MVC). Torque-frequency relationships were characterized over 6 frequencies from 20-120Hz. Results: NMES4 and NMES8 resulted in less decline in torque (42% and 41%) and generated more torque over the 100 contractions than NMES1 and NMES2 (53% and 50% decline in torque). Increasing frequency from 20-120Hz increased torque by 7, 13, 21 and 24% MVC, for NMES1, NMES2, NMES4 and NMES8, respectively. Perceived discomfort was highest during NMES8 . Conclusion: NMES4 and NMES8 reduced contraction fatigability and generated larger contractions across a range of frequencies than NMES1 and NMES2 . NMES8 produced the most discomfort, likely due to small electrodes and high current density. During NMES, more is not better and rotating pulses between 4-channels may be optimal to reduce contraction fatigability and produce larger contractions with minimal discomfort compared to conventional NMES configurations.

scholarly journals Time Course of Central and Peripheral Alterations after Isometric Neuromuscular Electrical Stimulation-Induced Muscle Damage

PLoS ONE ◽  
2014 ◽  
Vol 9 (9) ◽  
pp. e107298 ◽  
Author(s):  
Alexandre Fouré ◽  
Kazunori Nosaka ◽  
Jennifer Wegrzyk ◽  
Guillaume Duhamel ◽  
Arnaud Le Troter ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Muscle Damage ◽  
Time Course ◽  
Neuromuscular Electrical Stimulation

Turning on the central contribution to contractions evoked by neuromuscular electrical stimulation

2007 ◽  
Vol 103 (1) ◽  
pp. 170-176 ◽  
Author(s):  
J. C. Dean ◽  
L. M. Yates ◽  
D. F. Collins
Keyword(s):  
Electrical Stimulation ◽  
High Frequency ◽  
Muscle Fibers ◽  
Neuromuscular Electrical Stimulation ◽  
Motor Units ◽  
Stimulation Frequency ◽  
Central Mechanism ◽  
Triceps Surae ◽  
High Frequency Stimulation ◽  
Frequency Stimulation

Neuromuscular electrical stimulation can generate contractions through peripheral and central mechanisms. Direct activation of motor axons (peripheral mechanism) recruits motor units in an unnatural order, with fatigable muscle fibers often activated early in contractions. The activation of sensory axons can produce contractions through a central mechanism, providing excitatory synaptic input to spinal neurons that recruit motor units in the natural order. Presently, we quantified the effect of stimulation frequency (10–100 Hz), duration (0.25–2 s of high-frequency bursts, or 20 s of constant-frequency stimulation), and intensity [1–5% maximal voluntary contraction (MVC) torque generated by a brief 100-Hz train] on the torque generated centrally. Electrical stimulation (1-ms pulses) was delivered over the triceps surae in eight subjects, and plantar flexion torque was recorded. Stimulation frequency, duration, and intensity all influenced the magnitude of the central contribution to torque. Central torque did not develop at frequencies ≤20 Hz, and it was maximal at frequencies ≥80 Hz. Increasing the duration of high-frequency stimulation increased the central contribution to torque, as central torque developed over 11 s. Central torque was greatest at a relatively low contraction intensity. The largest amount of central torque was produced by a 20-s, 100-Hz train (10.7 ± 5.5 %MVC) and by repeated 2-s bursts of 80- or 100-Hz stimulation (9.2 ± 4.8 and 10.2 ± 8.1% MVC, respectively). Therefore, central torque was maximized by applying high-frequency, long-duration stimulation while avoiding antidromic block by stimulating at a relatively low intensity. If, as hypothesized, the central mechanism primarily activates fatigue-resistant muscle fibers, generating muscle contractions through this pathway may improve rehabilitation applications.

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