Transcranial Direct Current Stimulation Does Not Affect Lower Extremity Muscle Strength Training in Healthy Individuals: A Triple-Blind, Sham-Controlled Study

Abstract

The present study investigated the effects of anodal transcranial direct current stimulation (tDCS) on lower extremity muscle strength training in 24 healthy participants. In this triple-blind, sham-controlled study, participants were randomly allocated to the anodal tDCS plus muscle strength training (anodal tDCS) group or sham tDCS plus muscle strength training (sham tDCS) group. Anodal tDCS (2 mA) was applied to the primary motor cortex of the lower extremity during muscle strength training of the knee extensors and flexors. Training was conducted once every 3 days for 3 weeks (7 sessions). Knee extensor and flexor peak torques were evaluated before and after the 3 weeks of training. After the 3-week intervention, peak torques of knee extension and flexion changed from 155.9 to 191.1 Nm and from 81.5 to 93.1 Nm in the anodal tDCS group. Peak torques changed from 164.1 to 194.8 Nm on extension and from 78.0 to 85.6 Nm on flexion in the sham tDCS group. In both groups, peak torques of knee extension and flexion significantly increased after the intervention, with no significant difference between the anodal tDCS and sham tDCS groups. In conclusion, although the administration of eccentric training increased knee extensor and flexor peak torques, anodal tDCS did not enhance the effects of lower extremity muscle strength training in healthy individuals. The present null results have crucial implications for selecting optimal stimulation parameters for clinical trials.

Effect of transcranial direct current stimulation on exercise performance: A systematic review and meta-analysis

“…Studies assessed both men and women, with mean ± SD sample size per study was 14.4 ± 5.7 (from 6 to 24 participants) with a median of 12, aged from 17 to 42 years and different levels of physical activity/fitness (ranging from low active individuals to athletes). Regarding tDCS timing, 16 studies (72.7%) applied tDCS before exercise, three studies (13.6%) applied tDCS during exercise, one study (4.5%) applied tDCS both before and during exercise, one study (4.5%) applied tDCS over repeated sessions, and one (4.5%) during exercise training [58]. The effect of tDCS for improving exercise performance was assessed for muscle strength in 15 studies (68.2%), from which 10 (45.5%) used isometric, three (13.6%) used isokinetic, and two (9.1%) used dynamic strength exercise.…”

“…Furthermore, the use of tDCS outside the lab by the wider community may produce uncertain results due to inadequate electrode positioning, contact, impedance, and current flow. It should be noted that only two studies (9.1%) used tDCS for performance improvement over repeated sessions, with four [62] or seven sessions [58], and the safety for daily use of tDCS such as before/during training sessions is still to be evaluated. Therefore, the widespread application of tDCS outside the lab, such as with commercial devices, should be treated with significant caution until clear scientific evidence supports its safety and efficacy.…”

“…In addition, Maeda et al [58] applied a-tDCS over M1 during isokinetic training and found no effect of eccentric knee extension and flexion. Interestingly, the only two studies involving dynamic strength exercise showed contrasting results, where a single session of a-tDCS before exercise improved the number of maximum repetitions in elbow flexion exercise [65] and a single-session of strength training associated with a-tDCS did not change the maximal strength of the contralateral wrist extensors more than strength training or a-tDCS alone [66].…”

Cerebellar Transcranial Direct Current Stimulation Improves Maximum Isometric Force Production during Isometric Barbell Squats

“…Lower extremity muscle strength modulation has also been assessed through tDCS application, although results are rather inconclusive. For example, some results showed tDCS to be effective in modulating isometric muscle strength [10,14,15], whereas other studies provide evidence to the contrary [16][17][18]. It is of note that, among others stimulation sites, current density (mA/cm 2 ), as well as strength training background of participants all differ between studies, making interpretations difficult.…”

Acute Effects of High-Definition Transcranial Direct Current Stimulation on Foot Muscle Strength, Passive Ankle Kinesthesia, and Static Balance: A Pilot Study

“…However, several other studies showed the opposite results, reporting that tDCS may not significantly improve these functions. Maeda et al [37], for example, observed that anodal tDCS failed to enhance the lower extremity muscle strength in healthy participants. Similarly, studies also showed that anodal tDCS did not significantly elevate the maximal force production of knee extensors [38] nor enhance static balance ability [39].…”