Involuntary sustained firing of plantar flexor motor neurones: effect of electrical stimulation parameters during tendon vibration

Ricardo N O Mesquita,Janet L Taylor,Anthony J Blazevich,Benjamin Kirk

doi:10.1007/s00421-020-04563-7

Ricardo N O Mesquita, Janet L Taylor + Show 2 more

Open Access

https://doi.org/10.1007/s00421-020-04563-7

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Abstract

PurposeSimultaneous application of tendon vibration and neuromuscular electrical stimulation (NMES) induces an involuntary sustained torque. We examined the effect of different NMES parameters (intensity, pattern of stimulation and pulse width) on the magnitude of the evoked involuntary torque.MethodsPlantar flexor torque was recorded during 33-s Achilles tendon vibration with simultaneous 20-Hz NMES bouts on triceps surae (n = 20; 13 women). Intensity was set to elicit 10, 20 or 30% of maximal voluntary contraction torque (MVC), pulse width was narrow (0.2 ms) or wide (1 ms), and the stimulus pattern varied (5 × 2-s or 10 × 1-s). Up to 12 different trials were performed in a randomized order, and then repeated in those who produced a sustained involuntary torque after the cessation of vibration.ResultsSix of 7 men and 5 of 13 women produced a post-vibration sustained torque. Eight of 20 participants did not complete the 30% trials, as they were perceived as painful. Torque during vibration at the end of NMES and the increase in torque throughout the trial were significantly higher in 20 than 10% trials (n = 11; 9.7 ± 9.0 vs 7.1 ± 6.1% MVC and 4.3 ± 4.5 vs 3.6 ± 3.5% MVC, respectively). Post-vibration sustained torque was higher in wide pulse-width trials (5.4 ± 5.9 vs 4.1 ± 4.3% MVC). Measures of involuntary torque were not different between 20 and 30% trials (n = 8).ConclusionBouts of 5 × 2-s NMES with wide pulse width eliciting 20% MVC provides the most robust responses and could be used to maximise the production of involuntary torque in triceps surae.

Highlights

Neuromuscular electrical stimulation (NMES) and tendon vibration have been used independently (e.g. Magalhães et al 2013; Bochkezanian et al 2018b) and simultaneously (Magalhães and Kohn 2010; Trajano et al 2014; Bochkezanian et al 2018a; Kirk et al 2019) to induce motor unit (MU) activation, and muscle contractions
Trials with NMES intensity of 30% maximal voluntary contraction torque (MVC) were not performed by all participants, as 8 out
A significant main effect of “pulse width” in the ANOVA revealed that wide-pulse NMES evoked a greater Tsust than narrow-pulse NMES

Summary

Introduction

Neuromuscular electrical stimulation (NMES) and tendon vibration have been used independently (e.g. Magalhães et al 2013; Bochkezanian et al 2018b) and simultaneously (Magalhães and Kohn 2010; Trajano et al 2014; Bochkezanian et al 2018a; Kirk et al 2019) to induce motor unit (MU) activation, and muscle contractions. Other empirical evidence corroborates the contribution of centrally-mediated mechanisms This evidence includes greater levels of “extra torque” (Collins et al 2002; Lagerquist and Collins 2010) and electromyographic (EMG) activity (Arpin et al 2019) during wide- than narrow-pulse NMES, and the enhancement of H-reflexes, V- and F-wave amplitudes in association with extra torque development during NMES (Klakowicz et al 2006; Lagerquist and Collins 2010; Bergquist et al 2011a; Vitry et al 2019) and during tendon vibration (Magalhães et al 2013) or both simultaneously (Magalhães and Kohn 2010). Tendon vibration per se recruits low-threshold MUs (Grande and Cafarelli 2003) and the superposition of bursts of NMES may activate additional afferent fibres and activate a greater proportion of the MU pool (Collins et al 2001)

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