Author(s): ANGIUS, L., KAMIS, O., ESEN, O., SCOTT, L., ANDRUSHKO, J.W., COSGRAVE, T., GOODALL, S., Institution: NORTHUMBRIA UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 1374

INTRODUCTION:
Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that modulates neuronal activity by delivering a low-intensity electrical current between electrodes placed over the scalp. Acute tDCS has been shown to modulate corticospinal excitability [1] and recently to elicit ergogenic effects [2, 3]. However, the neurophysiological mechanisms underpinning these ergogenic effects remain largely unexplored. Therefore, the present study aimed to investigate the neuromuscular and neural responses during a fatiguing isometric task following acute tDCS.
METHODS:
In a randomised cross-over design, 19 healthy and active participants (14 ♂ and ♀ 5, age, 23 ± 5 years; height, 174 ± 8 cm; weight, 73 ± 8 kg) completed two experimental sessions receiving either anodal tDCS (EXP) or sham tDCS (SHAM). tDCS was delivered for 20 min at 2.0 mA to the primary motor cortex contralateral to the exercising limb in a resting state before exercise. Neuromuscular function and neural responses of the dominant knee extensors were monitored before and after tDCS administration. Neuromuscular function was quantified using maximal voluntary contraction (MVC), voluntary activation (VA), and electrical stimulation of the femoral nerve (contractile function, Qtw,pot). Neural responses were determined by measuring corticospinal excitability (CSE), short-interval intracortical inhibition (SICI), and excitability of the lumbar tract (LEP). Participants then performed a fatiguing isometric task of the knee extensors consisting of ten sets of 60-s duration at 15% of pre-task MVC. After each set, neuromuscular function was monitored to quantify the development of neuromuscular fatigue alongside perceived effort (RPE).
RESULTS:
Following tDCS, neuromuscular function remained unaltered, with no changes in MVC (p = 0.65), VA (p = 0.18), or Qtw,pot (p = 0.20). In contrast, the EXP condition was characterised by increased CSE (+14%, p < 0.05) and reduced SICI (−11%, p = 0.02), with no change in LEP (p = 0.26). During the fatiguing task, MVC and VA progressively declined (p < 0.01); however, these reductions were attenuated in the EXP, resulting in higher MVC (+6%, p < 0.01) and VA (+3%, p = 0.02) compared with SHAM. Qtw,pot declined similarly between conditions (p = 0.38). RPE increased progressively but remained lower in the EXP (p = 0.04).
CONCLUSION:
These findings indicate that acute tDCS does not enhance neuromuscular function during unfatigued maximal contractions but attenuates the development of neuromuscular fatigue during a submaximal fatiguing task. We suggest that the increase in corticospinal excitability and decrease in short-interval intracortical inhibition may contribute to the reduced central fatigue, thereby attenuating the development of neuromuscular fatigue. These results provide new evidence regarding the neurophysiological mechanisms underlying the ergogenic effects of acute tDCS.

References:
1. Stagg et al., 2018; 2. Angius et al., 2018; 3. Chinzara et al., 2022.