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

Abstract

This study aimed to examine the effects of single-session anodal high-definition transcranial direct current stimulation (HD-tDCS) on the strength of intrinsic foot muscles, passive ankle kinesthesia, and static balance. Methods: In this double-blinded self-controlled study, 14 healthy younger adults were asked to complete assessments of foot muscle strength, passive ankle kinesthesia, and static balance before and after a 20-minute session of either HD-tDCS or sham stimulation (i.e., control) at two visits separated by one week. Two-way repeated-measures analysis of variance was used to examine the effects of HD-tDCS on metatarsophalangeal joint flexor strength, toe flexor strength, the passive kinesthesia threshold of ankle joint, and the average sway velocity of the center of gravity. Results: All participants completed all study procedures and no side effects nor risk events were reported. Blinding was shown to be successful, with an overall accuracy of 35.7% in the guess of stimulation type (p = 0.347). No main effects of intervention, time, or their interaction were observed for foot muscle strength (p > 0.05). The average percent change in first-toe flexor strength following anodal HD-tDCS was 12.8 ± 24.2%, with 11 out of 14 participants showing an increase in strength, while the change following sham stimulation was 0.7 ± 17.3%, with 8 out of 14 participants showing an increase in strength. A main effect of time on the passive kinesthesia threshold of ankle inversion, dorsiflexion, and anteroposterior and medial-lateral average sway velocity of the center of gravity in one-leg standing with eyes closed was observed; these outcomes were reduced from pre to post stimulation (p < 0.05). No significant differences were observed for other variables between the two stimulation types. Conclusion: The results of this pilot study suggested that single-session HD-tDCS may improve the flexor strength of the first toe, although no statistically significant differences were observed between the anodal HD-tDCS and sham procedure groups. Additionally, passive ankle kinesthesia and static standing balance performance were improved from pre to post stimulation, but no significant differences were observed between the HD-tDCS and sham procedure groups. This may be potentially due to ceiling effects in this healthy cohort of a small sample size. Nevertheless, these preliminary findings may provide critical knowledge of optimal stimulation parameters, effect size, and power estimation of HD-tDCS for future trials aiming to confirm and expand the findings of this pilot study.

Effects of Combining High-Definition Transcranial Direct Current Stimulation with Short-Foot Exercise on Chronic Ankle Instability: A Pilot Randomized and Double-Blinded Study

“…Current intensity of the anode was set to 2 mA; return of current was evenly distributed between the four cathodes. Neuro-modeling results indicated that this montage induced electric fields that penetrated deep into the lower-extremity area of the primary sensorimotor cortex located along the longitudinal fissure [ 23 , 24 , 25 ].…”

Systematic Review of the Impact of Transcranial Direct Current Stimulation on the Neuromechanical Management of Foot and Ankle Physical Performance in Healthy Adults

“…Three studies used conventional tDCS applied over the sensorimotor cortex with an electrode size of 35 cm 2 (Tanaka et al, 2009 ; Zhou et al, 2018 ; Yamamoto et al, 2020 ). One study used a 4 × 1 ring high-definition tDCS (HD-tDCS), in which the anodal electrode was placed over Cz and was surrounded by four cathodal electrodes with a size of 1 cm 2 (Xiao et al, 2020 ). Three studies applied the current intensity of 2 mA (Tanaka et al, 2009 ; Zhou et al, 2018 ; Xiao et al, 2020 ), and one study applied the intensity of 1.5 mA (Yamamoto et al, 2020 ).…”

“…One study used a 4 × 1 ring high-definition tDCS (HD-tDCS), in which the anodal electrode was placed over Cz and was surrounded by four cathodal electrodes with a size of 1 cm 2 (Xiao et al, 2020 ). Three studies applied the current intensity of 2 mA (Tanaka et al, 2009 ; Zhou et al, 2018 ; Xiao et al, 2020 ), and one study applied the intensity of 1.5 mA (Yamamoto et al, 2020 ). The duration of tDCS was 10 min in two studies (Tanaka et al, 2009 ; Yamamoto et al, 2020 ) and 20 min in the other two studies (Zhou et al, 2018 ; Xiao et al, 2020 ).…”

“…Three studies applied the current intensity of 2 mA (Tanaka et al, 2009 ; Zhou et al, 2018 ; Xiao et al, 2020 ), and one study applied the intensity of 1.5 mA (Yamamoto et al, 2020 ). The duration of tDCS was 10 min in two studies (Tanaka et al, 2009 ; Yamamoto et al, 2020 ) and 20 min in the other two studies (Zhou et al, 2018 ; Xiao et al, 2020 ). The current density at the stimulation electrode was 0.043 or 0.057 mA/cm 2 with a total charge between 0.026 and 0.069 C/cm 2 .…”

Immediate Effects of Anodal Transcranial Direct Current Stimulation on Postural Stability Using Computerized Dynamic Posturography in People With Chronic Post-stroke Hemiparesis

“…Furthermore, other non-invasive methods of neuromodulation, such as prismatic adaptation, have been shown to activate compensatory postural adjustments to achieve improved body stability in the non-neurologically impaired (Bonaventura et al, 2020). Few studies, however, have investigated the effects of tDCS delivered to the leg motor area on balance and postural control in non-neurologically impaired individuals (Craig and Doumas, 2017;Yosephi et al, 2018;Xiao et al, 2020) and even more limited in individuals post-stroke (Sohn et al, 2013).…”