Acute Effects Of High-definition Transcranial Direct Current Stimulation On Toe Flexor Strength,Ankle Kinesthesia,and Static Balance

Purpose: The human foot is a very complex structure,refining as the foot core system,which plays an important role in walking,running,and jumping.However,foot injuries are common.Therefore,how to promote the foot function has an important research significance.Recently,studies have found that transcranial direct current stimulation(t DCS)can enhance foot function by increasing brain cortical excitability.This study thus aims to further investigate the acute effects of a single-session high-definition transcranial direct current stimulation(HD-t DCS)on foot muscle strength,ankle kinesthesia,and static balance.Methods: In this double-blinded sham-controlled study,fourteen healthy young college students at Shanghai University of Sport were recruited.A trained researcher was arranged to operate the t DCS.Participants were asked to receive a single-session anodal HD-t DCS(2m A stimulation for 20minutes)and sham stimulation(30 seconds of active stimulation only at the beginning)at one-week intervals.The metatarsophalangeal joint flexor strength,toe flexor strength,the passive kinesthesia threshold of ankle joint,and the variables of static balance were assessed before and immediately after a 20-minute session of stimulation.Two-way repeated measures ANOVA was used to examine the effects of HD-t DCS on the flexor strength of toes,the threshold of ankle passive kinesthesia,and static balance.Results: All participants completed the assessments and no unexpected side effects or adverse events were reported.The total correct rate of subjective guesses was 35.7%,showing successful blinding.Compared to pre-t DCS,a significant increase(11.0%)of the flexor strength of first toe,and decrease(14.7%)in the ankle varus passive kinesthesia was observed after real HD-t DCS(P < 0.05).Additionally,the antero-posterior and medio-lateral sway velocity of the center of gravity significantly decreased in standing with one foot and closed eyes after real HD-t DCS,9.0% and 11.1%,respectively,also decreased after sham stimulation,9.7% and 18.2%,respectively(P < 0.05).Conclusion: This study was the first to examine the effects of single-session anodal HD-t DCS designed to target the sensory-motor regions of the brain with respect to toe flexor strength,passive ankle kinesthesia,and static balance.No significant differences were observed with regard to such effects between anodal HD-t DCS and sham stimulation.This may be potentially due to ceiling effects in this study.The results suggested that anodal HD-t DCS may improve the toe flexor strength,passive ankle inversion kinesthesia,and static standing performance with one foot and closed eyes.It can be used as a potential means of enhancing foot function.Future research should further explore and clarify the effect of t DCS on foot and ankle physical performance and its underlying neurophysiological mechanisms.