RESUMEN

The present study examined the effects of transcranial direct current stimulation (tDCS) using Halo Sport on the time to exhaustion (TTE) in relation with muscle activities and corticomuscular coupling of agonist and antagonist muscles during a sustained isometric fatiguing contraction performed with the elbow flexors. Twenty healthy male college students were randomly assigned to tDCS group and control group. The two group participants performed two experimental sessions which consisted of pre-fatigue isometric maximal voluntary contraction (MVC), sustained submaximal voluntary contractions (30% maximal torque) performed to exhaustion, and post-fatigue MVC with the right elbow flexor muscles. Sham stimulation (90 s) and tDCS (20 min) were applied for control and tDCS group participants 20 min prior to the second session test, respectively. MVC strength in pre- and post-fatigue test, TTE, electroencephalogram (EEG), and electromyography (EMG) of biceps brachii (BB) and triceps brachii (TB) were recorded during the tests. It was found that tDCS using the Halo Sport device significantly increased TTE and thus improved muscular endurance performance. The improvement may be partly related to the improvement of neuromuscular efficiency as reflected by decrease of antagonistic muscle coactivation activities, which may be related to cortical originated central processing mechanism of neuromuscular activities.

RESUMEN

OBJECTIVE: During muscle fatigue, acute changes in the interaction between the sensorimotor cortex and peripheral neurons have been widely studied. However, it is still unclear about the effect of antagonist muscle prefatigue on corticomuscular coupling and central modulation. The purpose of this study was to investigate the changes in the magnitude of electroencephalogram-electromyography (EEG-EMG) coherence and phase synchronization index (PSI) induced by antagonistic muscle prefatigue. METHODS: Twelve young male volunteers conducted a 30-s long, nonfatiguing isometric elbow extension with a target force level of 20% maximum voluntary contraction (MVC) before and after a fatiguing sustained elbow flexion contraction at 20% MVC until task failure. Coherence and PSI between the EEG recorded over the sensorimotor cortex and the surface EMG of the triceps brachii (TB) muscle were quantified for the pre- and post-fatigue elbow extension contractions. RESULTS: Coherence and PSI in the gamma frequency band (35-60 Hz) were found significantly decreased in the postfatigue elbow extension contraction than the prefatigue contraction. The power of the EEG in the beta and gamma band were significantly increased, while the EMG power showed no significant changes when the antagonistic muscle was prefatigued. PSI in the gamma frequency band between the EMG of the TB muscle and the EEG were found significantly decreased during postfatigue elbow extension contraction compared with prefatigue contraction. CONCLUSION: Antagonistic muscle prefatigue led to significantly lower gamma band corticomuscular coherence and phase coupling during an isometric elbow extension position task. The lower corticomuscular coupling may indicate a central modulation mechanism of antagonist muscle prefatigue that related to decreased descending common drive or joint instability compensation modulation mechanism.

Asunto(s)

Asunto(s)

RESUMEN

The aim of this study was to examine coherence and phase synchronization between antagonistic elbow muscles and thus to explore the coupling and common neural inputs of antagonistic elbow muscles during sustained submaximal isometric fatiguing contraction. Fifteen healthy male subjects sustained an isometric elbow flexion at 20 % maximal level until exhaustion, while surface electromyographic signals (sEMG) were collected from biceps brachii (BB) and triceps brachii (TB). sEMG signals were divided into the first half (stage 1 with minimal fatigue) and second half (stage 2 with severe fatigue) of the contraction. Coherence and phase synchronization analysis was conducted between sEMG of BB and TB, and coherence value and phase synchronization index in alpha (8-12 Hz), beta (15-35 Hz) and gamma (35-60 Hz) frequency bands were obtained. Significant increase in EMG-EMG coherence and phase synchronization index in alpha and beta frequency bands between antagonistic elbow flexion muscles was observed all increased in stage 2 compared to stage 1. Coupling of EMG activities between antagonistic muscles increased as a result of fatigue caused by 20 % maximal level sustained isometric elbow flexion, indicating the increased interconnection between synchronized cortical neurons and the motoneuron pool of BB and TB, which may be cortical in origin. This increased coupling may help to maintain coactivation level so as to ensure joint stability on the basis of maintaining the joint force output.

Asunto(s)