Anodal transcranial direct current stimulation does not influence the neural adjustments associated with fatiguing contractions in a hand muscle

Abstract

Purpose The objective of the current study was to investigate the mechanisms responsible for the briefer time to failure of a submaximal contraction (C2) when performed 60 min after a similar contraction (C1), and the influence of anodal transcranial direct current stimulation (a-tDCS) applied over the motor cortex on these mechanisms. Methods In two sessions, ten adults sustained two isometric contractions (35% of maximum) to failure with the abductor pollicis brevis (APB). Before C2, either a-tDCS or sham stimulation was applied over the motor cortex. Fatigue-related changes in Hoffmann (H) and long-latency (LLR) reflexes, motor-evoked potential (MEP) induced by transcranial magnetic stimulation and associated silent period (SP), maximal motor wave (M max ), voluntary activation (VA), electromyographic (EMG) activity and peak force (PT 3 ) evoked by a 3 pulse-train (100 Hz) were investigated. ResultsThe results indicate that regardless of session, the time to failure was briefer (− 13%, p < 0.05) for C2 than C1, with no a-tDCS effect. During C1, MEP amplitude, SP duration and LLR amplitude increased, H-reflex amplitude did not change, and M max , VA and PT 3 decreased (p < 0.05). Except for EMG activity that was greater during C2 than C1 (p < 0.001), all variables were similar in C1 and C2 (p > 0.05), and recovered their initial values after the 60-min rest, except PT 3 . ConclusionsThe results of the current study indicate that a-tDCS did not influence corticospinal excitability and time to failure of C2 when performed with the APB. These observations may reflect a peripheral origin of the briefer C2 time to failure in the APB.

Transcranial Direct Current Stimulation Enhances Muscle Strength of Non-dominant Knee in Healthy Young Males

“…Furthermore, no significant change was noted in the activation level of the dominant flexor and extensor muscles after tDCS treatment, which was consistent with the results of muscle strength in this study. Some studies have determined that tDCS will not further heighten muscle function after it has reached a maximum level ( Lattari et al, 2016 ; Abdelmoula et al, 2019 ). Considering that the subjects selected in this study were all right leg dominant, the muscle activation level has reached the best state in high-intensity exercise, and in this state, the ability of tDCS to increase the number of motor unit recruitment to improve the muscle activation degree might be limited, resulting in no significant improvement in muscle strength performance.…”

Effects of Transcranial Direct Current Stimulation on Upper Limb Muscle Strength and Endurance in Healthy Individuals: A Systematic Review and Meta-Analysis

“…(2) There is no consensus on the effects of tDCS on upper limb motor performance, and the quantitative analysis samples included in this meta-analysis were too few, which would lead to the possibility of false negative or false-positive results in our synthesis. (3) In the study of upper limb endurance, only two articles (Abdelmoula et al, 2016(Abdelmoula et al, , 2018 focused on the dominant side. Although the results showed that tDCS had no significant effect on improving the muscle endurance of the dominant side of the upper limb, we were cautious about this result due to the lack of samples.…”

“…Similarly, in terms of muscle endurance, some studies found that tDCS had no effect on upper limb muscle endurance (Kan et al, 2013;Muthalib et al, 2013;Radel et al, 2017;Abdelmoula et al, 2018). For example, Abdelmoula et al (2018) found no significant change in time to exhaustion (TTE) after a-tDCS stimulation during thumb abduction at 35% MIVC by applying a 1.5 mA, 10 min tDCS stimulation to the left M1. In contrast, another study found that tDCS could increase the TTE (Cogiamanian et al, 2007;Williams et al, 2013;Abdelmoula et al, 2016).…”

“…Some studies have shown that tDCS is closely related to muscle strength and muscle endurance, especially of the upper limbs ( Lampropoulou and Nowicky, 2013 ; Krishnan et al, 2014 ; Abdelmoula et al, 2016 ; Frazer et al, 2017 ; Radel et al, 2017 ; Hikosaka and Aramaki, 2021 ). In terms of muscle strength, some studies found that tDCS had no effect on upper limb muscle strength ( Cogiamanian et al, 2007 ; Kan et al, 2013 ; Abdelmoula et al, 2016 , 2018 ). For example, Hikosaka and Aramaki (2021) found that the in the grip movement of 70% MIVC, there was no significant change in MIVC after anodal tDCS (a-tDCS) stimulation by applying 1.5 mA tDCS on the right primary motor cortex (M1) for 15 min.…”

Central nervous system physiology

“…However, a number of papers have drawn attention to the large variability in response to tDCS both between and within individuals, with several studies failing to observe any net effects ( Abdelmoula et al, 2019 ; Lopez-Alonso et al, 2014 ; Lopez-Alonso et al, 2015 ; Vannorsdall et al, 2016; Wiethoff et al, 2014 ; Wiltshire and Watkins, 2020 ; Wrightson et al, 2020 ). The discrepancies probably arise because, as noted above, the results of tDCS depend on so many factors, including the precise orientation neuronal/synaptic populations and current flow, the intensity of current in each individual, and the effects of ongoing (or past) brain states, or individual genetic susceptibility.…”