Facilitatory effect of tonic voluntary contraction on responses to motor cortex stimulation

doi:10.1016/0924-980X(95)00214-6

Electroencephalography and Clinical Neurophysiology/Electromyography and Motor Control

Volume 97, Issue 6, December 1995, Pages 451-454

Electroencephalograp...

https://doi.org/10.1016/0924-980X(95)00214-6 Get rights and content

Abstract

To investigate the mechanisms underlying the facilitation of responses to motor cortical stimulation produced by tonic voluntary contraction, we studied the facilitatory effects in 7 normal volunteers during different levels of muscle contraction. Responses were similarly facilitated by voluntary contraction with 3 forms of stimulation: magnetic cortical, electrical cortical, and foramen magnum level stimulation. At a high level of contraction, however, only magnetic responses were markedly facilitated. We conclude that the facilitation of responses to cortical stimulation induced by tonic voluntary contraction occurs mainly at the spinal level, but that cortical excitability changes also contribute to the enlargement of magnetic responses in the case of a high level of contraction.

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Calculating VATMS is more complicated than calculating VA with motor nerve stimulation because it is not appropriate to normalise the TMS-evoked SIT during a MVC to the resting twitch evoked by the same stimulus [63]. Since cortical and motoneuronal excitability are much lower at rest than during a voluntary contraction, the output evoked by TMS of the motor cortex cannot be compared between resting and active conditions [44,202]. This issue is circumvented by estimating the amplitude of the resting twitch rather than measuring it directly, by extrapolating the linear relationship between SIT and voluntary force at forces between 50–100% MVC [195].
The term fatigue is used to describe a distressing and persistent symptom of physical and/or mental tiredness in certain clinical populations, with distinct but ultimately complex, multifactorial and heterogenous pathophysiology. Chronic fatigue impacts on quality of life, reduces the capacity to perform activities of daily living, and is typically measured using subjective self-report tools. Fatigue also refers to an acute reduction in the ability to produce maximal force or power due to exercise. The classical measurement of exercise-induced fatigue involves neuromuscular assessments before and after a fatiguing task. The limitations and alternatives to this approach are reviewed in this paper in relation to the lower limb and whole-body exercise, given the functional relevance to locomotion, rehabilitation and activities of daily living. It is suggested that under some circumstances, alterations in the central and/or peripheral mechanisms of fatigue during exercise may be related to the sensations of chronic fatigue. As such, the neurophysiological correlates of exercise-induced fatigue are briefly examined in two clinical examples where chronic fatigue is common: cancer survivors and people with multiple sclerosis. This review highlights the relationship between objective measures of fatigability with whole-body exercise and perceptions of fatigue as a priority for future research, given the importance of exercise in relieving symptoms of chronic fatigue and/or overall disease management. As chronic fatigue is likely to be specific to the individual and unlikely to be due to a simple biological or psychosocial explanation, tailored exercise programmes are a potential target for therapeutic intervention.
Le terme fatigue est utilisé pour décrire un symptôme pénible et persistant de fatigue physique et/ou mentale dans certaines populations cliniques, avec une pathophysiologie distincte, mais finalement complexe, multifactorielle et hétérogène. La fatigue chronique a des répercussions sur la qualité de vie, réduit la capacité d’effectuer des activités de la vie quotidienne et est généralement mesurée à l’aide d’outils subjectifs d’auto-évaluation. La fatigue se réfère également à une réduction aiguë de la capacité à produire une force ou puissance maximale au cours de l’exercice. La mesure classique de la fatigue induite par l’exercice implique des évaluations neuromusculaires avant et après une tâche fatigante. Les limites et les solutions de rechange à cette approche sont revues dans cet article en rapport avec l’exercice du membre inférieur et corps-entier, étant donné la pertinence fonctionnelle de cela en ce qui concerne la locomotion, la réadaptation et les activités de la vie quotidienne. Nous suggérons que les altérations des mécanismes centraux et/ou périphériques de la fatigue au cours de l’exercice puissent être liées aux sensations de fatigue chronique. Ainsi, les corrélats neurophysiologiques de la fatigue induite par l’effort sont brièvement examinés dans deux exemples cliniques : les survivants du cancer et les personnes atteintes de sclérose en plaques. Cette étude met en évidence la relation entre les mesures objectives de fatigabilité liée à l’exercice corps-entier et les perceptions de fatigue comme une priorité de recherche pour le futur, étant donné l’importance de l’exercice pour soulager les symptômes de la fatigue chronique et/ou la gestion globale de la maladie. Comme la fatigue chronique est susceptible d’être spécifique à l’individu et qu’il est peu probable qu’elle est due à une simple explication biologique ou psychosociale, des programmes d’exercices adaptés représentent une stratégie potentielle de traitement.
Reduced cortical voluntary activation during bilateral knee extension
2017, Human Movement Science
Reduced neural drive is mainly thought to explain the bilateral deficit phenomenon, i.e. the difference in maximal isometric voluntary contraction (MVC) between unilateral and bilateral contractions. The aim of the present study was to further document if bilateral knee extension is associated with changes in voluntary activation level assessed by both peripheral nerve electrical stimulation and transcranial magnetic stimulation.
Fourteen subjects performed unilateral and bilateral knee extensions with both superimposed femoral electrical nerve stimulation and transcranial magnetic stimulation in order to assess voluntary activation (VA_FNES) and cortical voluntary activation (VA_TMS), respectively.
There was no difference in MVC force of the tested leg when involved in unilateral and bilateral knee extensions (p = 0.87). However, a significantly reduced VA_FNES (−2.1 ± 2.4%; p = 0.01) and VA_TMS (−1.6 ± 2.7%; p = 0.04) have been evidenced during bilateral knee extension.
It is hypothesized that counterbalances could have masked the decrease of voluntary activation during bilateral contraction.
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Citation Excerpt :
Moreover, differences in task-dependent MEP facilitations were noted between the FDI and ADM muscles (Ni et al., 2006). An important source of MEP facilitation in the primary motor cortex has also been described (Thompson et al., 1991; Mazzocchio et al., 1994; Ugawa et al., 1995; Davey et al., 1996). We interpreted our results to be due to a cortical rather than a spinal mechanism.
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MEP gain revealed a significant difference between the patients and healthy control subjects in contrast to MEP area and MEP/CMAP area ratio. The diagnostic utility of MEP gain was comparable with that of TST and superior to that of DTI.
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This study aimed to evaluate the intra- and inter-day reliability of transcranial magnetic stimulation (TMS)-related measurements recorded from the tibialis anterior (TA) muscle. Thirteen healthy young men and women (23 ± 4 years) performed 3 testing sessions to assess intra- (i.e., two sessions performed the same day) and inter-day (i.e. two sessions performed one week apart) reliability of (i) dorsiflexion cortical maximal voluntary activation level (VA_TMS), (ii) TA corticospinal excitability assessed through the amplitude of the motor evoked potentials (MEP) recorded during 100, 75 and 50% maximal voluntary contractions (MVC), and (iii) intracortical inhibition investigated via the cortical silent period (CSP) recorded at the same % MVC. Absolute (i.e., coefficient of variation (CV) and standard error of the mean (SEM)), and relative (i.e., intraclass correlation coefficients (ICC)) reliability parameters were calculated. VA_TMS demonstrated excellent intra- and inter-day reliabilities (ICC: 0.80 and 0.99; CV: 1.7 and 0.8%, respectively). MEPs and CSPs presented moderate to excellent intra- and inter-day reliabilities, while input-output curves extracted parameters presented highly variable outcomes. These results suggest that most TA corticospinal measurements during voluntary contractions can be used to quantify corticospinal adaptations after acute (e.g. fatigue) or long term (e.g. training) interventions.
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2024, Middle East Journal of Rehabilitation and Health Studies

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Short communicationFacilitatory effect of tonic voluntary contraction on responses to motor cortex stimulation

Abstract

Electroenceph. clin. Neurophysiol.

Neurosci. Lett.

Electroenceph. clin. Neurophysiol.

Electroenceph. clin. Neurophysiol.

Response of arm flexor muscles to magnetic and electrical brain stimulation during shortening and lengthening tasks in man

J. Physiol. (Lond.)

The site of facilitation of the response to cortical stimulation during voluntary contraction in man

J. Physiol. (Lond.)

Evidence concerning the site of facilitation of phrenic motoneurone output in response to volitional inspiration in man

J. Physiol. (Lond.)

Short communication
Facilitatory effect of tonic voluntary contraction on responses to motor cortex stimulation