Cortical voluntary activation can be reliably measured in human wrist extensors using transcranial magnetic stimulation.
ABSTRACT A twitch interpolation technique using transcranial magnetic stimulation (TMS) was recently developed to measure motor cortical drive to human elbow flexors. Here, we described studies designed to test the applicability and reliability of the technique for the human wrist extensors and to provide new evidence regarding the sensitivity of the technique to inadvertent antagonist activation.
Study 1: we measured amplitudes of superimposed twitches (SITs) produced by TMS during wrist extension at intensities from rest to maximal voluntary contraction on two occasions (n=9). Study 2: we assessed the impact of inadvertent antagonist activation by TMS on measurement of voluntary activation using a muscle potentiation technique to increase mechanical efficiency of the wrist flexors (n=6).
The SITs decreased linearly between 25% and 100% MVC and voluntary activation could be reliably estimated across days (ICC(2,1)=0.963, p<0.001). Prior potentiation of the wrist flexors had little impact on extension SITs and voluntary activation.
TMS allows valid and reliable measurement of voluntary activation of the wrist extensors.
TMS can be used to assess effects of supraspinal fatigue, pathology and rehabilitation interventions on cortical activation in upper limb muscle groups.
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ABSTRACT: The study compared peripheral magnetic with electrical stimulation of the biceps brachii m. (BB) in the single pulse Interpolation Twitch Technique (ITT). 14 healthy participants (31±7 years) participated in a within-subjects repeated-measures design study. Single, constant-current electrical and magnetic stimuli were delivered over the motor point of BB with supramaximal intensity (20% above maximum) at rest and at various levels of voluntary contraction. Force measurements from right elbow isometric flexion and muscle electromyograms (EMG) from the BB, the triceps brachii m. (TB) and the abductor pollicis brevis m. (APB) were obtained. The twitch forces at rest and maximal contractions, the twitch force-voluntary force relationship, the M-waves and the voluntary activation (VA) of BB between magnetic and electrical stimulation were compared. The mean amplitude of the twitches evoked at MVC was not significantly different between electrical (0.62 ± 0.49 N) and magnetic (0.81 ± 0.49 N) stimulation (p > 0.05), and the maximum VA of BB was comparable between electrical (95%) and magnetic (93%) stimulation (p > 0. 05). No differences (p >0.05) were revealed in the BB M-waves between electrical (13.47 ± 0.49 mV.ms) and magnetic (12.61 ± 0.58 mV.ms) stimulation. The TB M-waves were also similar (p > 0.05) but electrically evoked APB M-waves were significantly larger than those evoked by magnetic stimulation (p < 0.05). The twitch-voluntary force relationship over the range of MVCs was best described by non-linear functions for both electrical and magnetic stimulation. The electrically evoked resting twitches were consistently larger in amplitude than the magnetically evoked ones (mean difference 3.1 ± 3.34 N, p < 0.05). Reduction of the inter-electrodes distance reduced the twitch amplitude by 6.5 ± 6.2 N (p < 0.05). The fundamental similarities in voluntary activation assessment of BB with peripheral electrical and magnetic stimulation point towards a promising new application of peripheral magnetic stimulation as an alternative to the conventional ITT for the assessment of BB voluntary activation.Journal of sports science & medicine 01/2012; 11(4):709-18. · 0.89 Impact Factor
- European Neuropsychopharmacology 09/2011; 21. · 4.60 Impact Factor
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ABSTRACT: Abstract The aim of this commentary is to provide a brief overview of transcranial magnetic stimulation (TMS) and highlight how this technique can be used to investigate the acute and chronic responses of the central nervous system to exercise. We characterise the neuromuscular responses to TMS and discuss how these measures can be used to investigate the mechanisms of fatigue in response to locomotor exercise. We also discuss how TMS might be used to study the corticospinal adaptations to resistance exercise training, with particular emphasis on the responses to shortening/lengthening contractions and contralateral training. The limited data to date suggest that TMS is a valuable technique for exploring the mechanisms of central fatigue and neural adaptation.European journal of sport science. 01/2014; 14(sup1):S332-S340.