Increased leg muscle fatigability during 2 mA and 4 mA transcranial direct current stimulation over the left motor cortex

Exp Brain Res. 2020 Feb;238(2):333-343. doi: 10.1007/s00221-019-05721-w. Epub 2020 Jan 9.

Abstract

Transcranial direct current stimulation (tDCS) using intensities ≤ 2 mA on physical and cognitive outcomes has been extensively investigated. Studies comparing the effects of different intensities of tDCS have yielded mixed results and little is known about how higher intensities (> 2 mA) affect outcomes. This study examined the effects of tDCS at 2 mA and 4 mA on leg muscle fatigability. This was a double-blind, randomized, sham-controlled study. Sixteen healthy young adults underwent tDCS at three randomly ordered intensities (sham, 2 mA, 4 mA). Leg muscle fatigability of both legs was assessed via isokinetic fatigue testing (40 maximal reps, 120°/s). Torque- and work-derived fatigue indices (FI-T and FI-W, respectively), as well as total work performed (TW), were calculated. FI-T of the right knee extensors indicated increased fatigability in 2 mA and 4 mA compared with sham (p = 0.01, d = 0.73 and p < 0.001, d = 1.61, respectively). FI-W of the right knee extensors also indicated increased fatigability in 2 mA and 4 mA compared to sham (p = 0.01, d = 0.57 and p < 0.001, d = 1.12, respectively) and 4 mA compared with 2 mA (p = 0.034, d = 0.37). tDCS intensity did not affect TW performed. The 2 mA and 4 mA tDCS intensities increased the fatigability of the right knee extensors in young, healthy participants, potentially from altered motor unit recruitment/discharge rate or cortical hyperexcitability. Despite this increase in fatigability, the TW performed in both these conditions was not different from sham.

Keywords: High intensity; Isokinetic task; Muscle fatigue; Non-invasive brain stimulation; Transcranial direct current stimulation.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Double-Blind Method
  • Female
  • Humans
  • Leg / physiology*
  • Male
  • Motor Activity / physiology*
  • Motor Cortex / physiology*
  • Muscle Fatigue / physiology*
  • Muscle, Skeletal / physiology*
  • Placebos
  • Transcranial Direct Current Stimulation*
  • Young Adult

Substances

  • Placebos