PURPOSE:This study aimed to investigate the effects of individualized dose-controlled high-definition transcranial direct current stimulation (HD-tDCS) in combination with foot core exercise (FCE) on functional supraspinal network characteristics and sensorimotor function in individuals with chronic ankle instability (CAI). METHODS:In this double-blind, randomized controlled trial, 34 participants were allocated into 2 groups: individualized dose-controlled HD-tDCS combined with FCE and sham stimulation combined with FCE (control group). Participants received 20 min of stimulation concurrent with FCE, 3 times per week over a 4-week period. Assessments included task-related functional magnetic resonance imaging and ankle force sense, conducted at baseline and post-intervention. RESULTS:Compared with baseline and the control group, the individualized dose-controlled HD-tDCS combined with FCE reduced task-related cortical activation in the bilateral inferior parietal lobule and the right supplementary motor area (rSMA) and increased functional connectivity (FC) between the left inferior parietal lobule and the right putamen. Additionally, improved dorsiflexion, inversion, and eversion force senses were observed. Besides, changes in force sense were negatively correlated with changes in signal intensities in the right inferior parietal lobule and rSMA, and marginally significantly associated with changes in FC between the left inferior parietal lobule and right putamen. CONCLUSION:A 4-week intervention of individualized dose-controlled HD-tDCS combined with FCE effectively reduced cortical activation during ankle motor tasks, strengthened FC within relevant supraspinal networks, and enhanced sensorimotor function in individuals with CAI.

OBJECTIVES:Chronic ankle instability (CAI) is not only associated with those peripheral neuromuscular impairments but also with the functional changes in the supraspinal regions. Nevertheless, the characteristics of the cortical elements in CAI remain poorly understood. This study aimed to examine the dynamics of resting-state BOLD and ankle-related functional performance in recreational athletes with CAI, as well as explore the associations between neural fluctuations and ankle functional performance. METHODS:This cross-sectional design study recruited 82 participants, comprising 41 active recreational athletes with CAI (CAI group) and 41 active recreational athletes without CAI (Control group). Data on joint position sense, one-leg standing balance, and resting-state fMRI were collected from both groups. A two-sample t-test was used to determine the difference in amplitude of low-frequency fluctuation (ALFF), fractional ALFF (fALFF), and regional homogeneity (ReHo) between the two groups. Linear regression analysis evaluated the associations between functional performance and dynamics of resting-state BOLD in the two groups. RESULTS:Compared with control group, athletes with CAI had lower ALFF values in the bilateral supplementary motor area and reduced ReHo values in the right precentral gyrus and postcentral gyrus, while higher ALFF and ReHo values in the right cerebellum. Moreover, athletes with CAI had lower fALFF values in the left superior frontal gyrus and the right superior frontal gyrus than controls. The sway velocities of center of pressure in the one-leg standing with eyes closed condition were negatively associated with ALFF and ReHo values in the right cerebellum cluster. CONCLUSIONS:Athletes with severely right-sided CAI had different neural fluctuations compared with controls. Elevated ALFF and ReHo values in the right cerebellum cluster were associated with balance control, suggesting that high ipsilateral cerebellar activity and homogeneity may compensate for balance control in athletes with CAI.

This study aimed to investigate postural sway complexity in chronic ankle instability (CAI) in static postural control and its relationship with the duration of ankle instability. 61 participants were recruited, including 35 CAI and 26 healthy controls (HC). Right leg standing balance was assessed in eyes open (EO) and eyes closed (EC) conditions for 20s. Multiscale entropy was used to quantify the complexity of center of pressure fluctuations in the anterior-posterior (AP) and medial-lateral (ML) directions. One-way ANOVA was used to compare the differences in postural sway complexity between the two groups. Compared with HC, the AP (F = 6.812, p = 0.012, η2 = 0.133) and ML sway complexity (F = 4.164, p = 0.047, η2 = 0.087) in EO condition was significantly lower in CAI group, but not in EC (ML: F = 1.229, p = 0.274, η2 = 0.027; AP: F = 2.398, p = 0.129, η2 = 0.052). The duration of ankle instability was correlated with ML sway complexity in EC condition in CAI group (r = -0.484, p = 0.023). This indicates that CAIs have poor adaptability to stressors, and multiscale entropy can serve as a potential indicator for identifying impaired postural control with eyes open in CAI.

This study investigated the effects of running-induced fatigue on ankle plantar–dorsiflexion performance and explored the underlying neuromuscular control mechanisms. Twenty-four male participants performed a right-sided ankle plantar–dorsiflexion task before and after running-induced fatigue, with simultaneous recordings of ankle peak torque, electroencephalography signals from the primary motor cortex (M1; Cz, C1, C2) and other brain regions, and electromyography signals from the tibialis anterior (TA) and medial gastrocnemius (MG). Ankle peak torque was used to assess plantar–dorsiflexion performance. Beta- and gamma-band corticocortical coherence (CCC) was used to evaluate brain network connectivity, while partial directed coherence (PDC) was applied to analyze the brain–muscle network. In the brain network, fatigue significantly reduced beta-band CCC for C1-Cz electrode pair (p = 0.022) during dorsiflexion, beta band for C2-Cz (p = 0.014), and gamma band for C1-Cz (p = 0.003) during plantarflexion. In the brain–muscle network, fatigue significantly decreased gamma-band PDC for TA-Cz (p = 0.007) during dorsiflexion and for MG-Cz (p = 0.010) during plantarflexion in the ascending pathway. The declines in ankle peak torques after fatigue were positively correlated with reduced gamma-band PDC in the ascending pathway (p < 0.034). These findings suggest that running-induced fatigue significantly reduced functional connectivity within bilateral M1 regions and the ascending pathway of the brain–muscle network during unilateral ankle plantar–dorsiflexion, with weakened connectivity in the ascending pathway linked to decreased ankle force output.

Objectives This study aimed to investigate the effect of fatigue induced by local- and general-muscular exercise on brain network efficiency, corticospinal and neuromuscular excitability. Methods Twenty-four participants randomly performed two different fatigue protocols (i.e., locally induced vs generally induced) separated by 5–7 days. Local fatigue was provided with maximum isokinetic plantar dorsiflexion, and general fatigue was provided with a running exercise on a treadmill at a personalized constant velocity. M-wave, H-reflex, and the resting-state electroencephalography signal, were recorded before and after local and general fatigue. Results Compared with local fatigue, fatigue induced by general muscular exercise can significantly increase clustering coefficient (p = 0.003), global efficiency (p = 0.001) and local efficiency (p = 0.005) in the beta band relative to the baseline values. The two fatigue protocols can significantly decrease maximal M-wave (Mmax, p < 0.001), maximal H-reflex (Hmax, p < 0.001), Hmax/Mmax (p = 0.001) and level of activation (p < 0.001). Conclusion The two different fatigue protocols can decrease peripheral neuromuscular excitability and affect spinal fatigue. General fatigue can promote the integration of local and global efficiency by strengthening the functional connectivity of the brain network to optimize resource allocation and resist the negative effects of fatigue.

OBJECTIVE:To explore whether there are differences in sensorimotor function between sexes in individuals with and without chronic ankle instability (CAI). DESIGN:Cross-sectional study. SETTING:Laboratory. PARTICIPANTS:50 (26 males/24 females) individuals with CAI and 40 (17 males/23 females) healthy controls (HC). MAIN OUTCOME MEASURES:Ankle muscle strength and proprioception were assessed using an isokinetic dynamometer. Static balance performance was assessed by a one-leg standing task, and dynamic balance performance was tested using the Y-Balance test. RESULTS:Compared with healthy controls, both males and females with CAI exhibited worse proprioception and balance control, but no difference in muscle strength. A significant group and sex interaction effect was observed of force sense in the dorsiflexion direction (F = 5.14, p = 0.026, ηp2 = 0.057). Post-hoc analysis showed that, the absolute error of force sense in males was significantly larger than females in the CAI group (p < 0.001), while there was no difference in the HC (p = 0.536). CONCLUSION:This finding indicated that among individuals with CAI, males are more likely to experience a greater impairment in the dorsiflexion direction of force sense than females. Future rehabilitation programs should consider targeted proprioceptive interventions for males to address this deficit effectively.

This study aimed to investigate the effects of four-week individualized transcranial direct current stimulation (tDCS) combined with foot core exercise (FCE) on foot and ankle sensorimotor function and postural control in individuals with chronic ankle instability (CAI). Thirty-four CAI individuals were randomly assigned to a tDCS combined with FCE group (tDCS group, n = 17) and a sham stimulation combined with FCE group (control group, n = 17). All participants received individualized stimulation combined with FCE and sham stimulation combined with FCE, respectively, three times a week for 20 min per session over four weeks. Ankle strength, joint position sense, and static and dynamic postural control were assessed at baseline and post-intervention. Compared with the control group and baseline, individualized tDCS combined with FCE significantly increased the relative peak torque of plantarflexion, reduced the absolute error of ankle eversion position sense, and decreased the average sway velocity of the center of pressure during single-leg standing with eyes closed in CAI individuals (p values ranging from < 0.001 to 0.016). Four weeks of individualized tDCS combined with FCE can effectively improve foot and ankle sensorimotor function and static postural control in CAI individuals.

OBJECTIVES:This study aims to understand the supraspinal regulation of balance control in chronic ankle instability (CAI) by characterizing the large-scale communication and interaction via brain functional network topology in CAI and establish the association between topological properties and dynamic balance performance. METHODS:In this cross-sectional design study, 40 CAI individuals and 39 healthy control (HC) individuals were enrolled. To assess the dynamic balance, the Y-balance test was utilized. To explore the topological structure of brain networks, graph theory was used to analyze resting-state functional magnetic resonance imaging data. RESULTS:The CAI group had lower normalized reach distances in the Y-balance test than HC. Compared with HC, CAI exhibited remarkably lower nodal degree centrality and higher nodal shortest path length (NLp) within the sensorimotor network (SMN), particularly in the precentral gyrus, temporal cortex, and presupplementary motor area of the right hemisphere. CAI showed reduced NLp and increased nodal efficiency in the posterior cingulate cortex of the left hemisphere, a hub region of the default mode subnetwork. In CAI, high degree centrality and low NLp in the precentral gyrus of the right hemisphere were substantially correlated to poor performance of the Y-balance test, but not in HC. CONCLUSIONS:CAI individuals demonstrated diminished regional processing capability within the SMN and a potential compensatory increase in nodal efficiency within the DMN, which are critical to maintain safe balance in this cohort. These alterations in supraspinal networks could be an effective target for rehabilitation and management in CAI.

This study aimed to investigate the effects of high-definition transcranial direct current stimulation on ankle force sense and underlying cerebral hemodynamics. Sixteen healthy adults (8 males and 8 females) were recruited in the study. Each participant received either real or sham high-definition transcranial direct current stimulation interventions in a randomly assigned order on 2 visits. An isokinetic dynamometer was used to assess the force sense of the dominant ankle; while the functional near-infrared spectroscopy was employed to monitor the hemodynamics of the sensorimotor cortex. Two-way analyses of variance with repeated measures and Pearson correlation analyses were performed. The results showed that the absolute error and root mean square error of ankle force sense dropped more after real stimulation than after sham stimulation (dropped by 23.4% vs. 14.9% for absolute error, and 20.0% vs. 10.2% for root mean square error). The supplementary motor area activation significantly increased after real high-definition transcranial direct current stimulation. The decrease in interhemispheric functional connectivity within the Brodmann's areas 6 was significantly correlated with ankle force sense improvement after real high-definition transcranial direct current stimulation. In conclusion, high-definition transcranial direct current stimulation can be used as a potential intervention for improving ankle force sense. Changes in cerebral hemodynamics could be one of the explanations for the energetic effect of high-definition transcranial direct current stimulation.

ABSTRACTThe relationship between structural changes in the cerebral gray matter and diminished balance control performance in patients with chronic ankle instability (CAI) has remained unclear. This paper aimed to assess the difference in gray matter volume (GMV) between participants with CAI and healthy controls (HC) and to characterize the role of GMV in the relationship between disease duration and balance performance in CAI. 42 participants with CAI and 33 HC completed the structural brain MRI scans, one‐legged standing test, and Y‐balance test. Regional GMV was measured by applying voxel‐based morphometry methods. The result showed that, compared with HC, participants with CAI exhibited lower GMV in multiple brain regions (familywise error [FWE] corrected p < 0.021). Within CAI only, but not in HC, lower GMV in the thalamus (β = −0.53, p = 0.003) and hippocampus (β = −0.57, p = 0.001) was associated with faster sway velocity of the center of pressure (CoP) in eyes closed condition (i.e., worse balance control performance). The GMV in the thalamus (percentage mediated [PM] = 32.02%; indirect effect β = 0.119, 95% CI = 0.003 to 0.282) and hippocampus (PM = 33.71%; indirect effect β = 0.122, 95% CI = 0.005 to 0.278) significantly mediated the association between the disease duration and balance performance. These findings suggest that the structural characteristics of the supraspinal elements is critical to the maintenance of balance control performance in individuals suffering from CAI, which deserve careful consideration in the management and rehabilitation programs in this population.

The effects of a 12-week gait retraining program on the adaptation of the medial gastrocnemius (MG) and muscle-tendon unit (MTU) were investigated. 26 runners with a rearfoot strike pattern (RFS) were randomly assigned to one of two groups: gait retraining (GR) or control group (CON). MG ultrasound images, marker positions, and ground reaction forces (GRF) were collected twice during 9 km/h of treadmill running before and after the intervention. Ankle kinetics and the MG and MTU behavior and dynamics were quantified. Runners in the GR performed gradual 12-week gait retraining transitioning to a forefoot strike pattern. After 12-week, (1) ten participants in each group completed the training; eight participants in GR transitioned to non-RFS with reduced foot strike angles; (2) MG fascicle contraction length and velocity significantly decreased after the intervention for both groups, whereas MG forces increased after intervention for both groups; (3) significant increases in MTU stretching length for GR and peak MTU recoiling velocity for both groups were observed after the intervention, respectively; (4) no significant difference was found for all parameters of the series elastic element. Gait retraining might potentially influence the MG to operate at lower fascicle contraction lengths and velocities and produce greater peak forces. The gait retraining had no effect on SEE behavior and dynamics but did impact MTU, suggesting that the training was insufficient to induce mechanical loading changes on SEE behavior and dynamics.

This study systematically reviews the literature on transcranial direct current stimulation (tDCS) interventions for lower-limb endurance performance in healthy adults and provides a summary of the effects and underlying mechanisms of tDCS on lower-limb endurance performance. Systematic searches were performed in PubMed, Web of Science, EBSCO, and ScienceDirect. The risk of bias was assessed using the Cochrane risk of bias assessment tool. The electronic search totaled 341 studies. Twenty-one studies were included in the review after screening. The results show that tDCS effectively improved time to task failure (TTF), increased blood lactate accumulation, and reduced the rating of perceived exertion during cycling. However, the tDCS failed to significantly improve the TTF, relieve muscle pain, and reduce fatigue indices during single-joint fatigue tasks in the knee. Moreover, tDCS intervention caused the effective improvement of the overall lower-limb endurance performance but exerted no uniformly conclusive effect on knee endurance performance. This finding can be partly attributed to varying stimulation protocols across studies. Future studies may focus on the effects of the application of stimulation protocols, such as multitarget stimulation and personalized dosage, to develop targeted stimulation protocols.

Background:Foot kinematics,such as excessive eversion and malalignment of the hindfoot,are believed to be associated with running-related injuries.The maj ority of studies to date show that different foot strike patterns influence these specific foot and ankle kinematics.However,technical deficiencies in traditional motion capture approaches limit knowledge of in vivo joint kinematics with respect to rearfoot and forefoot strike patterns（RFS and FFS,respectively）.This study uses a high-speed dual fluoroscopic imaging system（DFIS） to determine the effects of different foot strike patterns on 3D in vivo tibiotalar and subtalar joints kinematics.Methods:Fifteen healthy male recreational runners underwent foot computed tomography scanning for the construction of 3-dimensional models.A high-speed DFIS（100 Hz） was used to collect 6 degrees of freedom kinematics for participants’ tibiotalar and subtalar joints when they adopted RFS and FFS in barefoot condition.Results:Compared with RFS,FFS exhibited greater internal rotation at 0%-20% of the stance phase in the tibiotalar joint.The peak internal rotation angle of the tibiotalar joint under FFS was greater than under RFS（p ＜0.001,Cohen’s d=0.92）.RFS showed more dorsiflexion at 0%-20% of the stance phase in the tibiotalar joint than FFS.RFS also presented a larger anterior translation（p ＜0.001,Cohen’s d=1.28） in the subtalar joint at i nitial contact than FFS.Conclusion:Running with acute barefoot FFS increases the internal rotation of the tibiotalar joint in the early stance.The use of high-speed DFIS to quantify the movement of the tibiotalar and subtalar joint was critical to revealing the effects of RF S and FFS during running.

This study aimed to evaluate the effect of combining high-definition transcranial direct current stimulation (HD-tDCS) with foot core exercise (FCE) on dynamic postural stability and to determine whether the improvement achieved through this mix-type intervention outperforms the intervention of HD-tDCS and FCE alone. Sixty healthy males were recruited and randomly divided into four groups: (1) HD-tDCS + FCE group (HD-tDCS combined with FCE intervention); (2) s-tDCS + FCE (sham tDCS combined with FCE intervention); (3) HD-tDCS group which only received HD-tDCS; (4) FCE group which only performed FCE. All participants received a four-week intervention (3 times a week, 20 min each time). The Y-balance task was completed before and after the intervention. The maximum reaching distance was recorded, and the data of the center of pressure (COP) were collected by a three-dimensional force plate to calculate COP displacement and velocity. No significant change in COP displacement was found among the four groups. However, the COP velocity decreased significantly in the posteromedial direction after HD-tDCS + FCE intervention compared with the baseline. The maximum reach distance was significantly increased after HD-tDCS + FCE intervention in the posteromedial (p < 0.001) and posterolateral (p < 0.001) directions of the Y balance task compared with the baseline, and the extent of increase was greater than that in the three other groups. The intervention of HD-tDCS combined with FCE may exert a synergistic effect and more effectively improve dynamic postural stability.

ObjectiveThis study aimed to investigate differences in cortical activation between individuals with and without chronic ankle instability (CAI) during a dorsi-plantarflexion task and further explore its association with sensorimotor function.MethodsIn this cross-sectional study, 62 participants were recruited, including 31 adults with CAI and 31 healthy adults. Sensorimotor functions, including joint position sense and force sense, were tested using absolute error associated with joint position reproduction and force reproduction tasks. A block design was used to collect task-state functional magnetic resonance imaging by using a custom-built, Magnetic resonance imaging-compatible device during a dorsi-plantarflexion task.ResultsIndividuals with CAI showed significantly worse joint position sense and force sense in all four movement directions than those without CAI. Chronic ankle instability is significantly associated with lower cortical activation in the sensorimotor network, mainly including the right postcentral gyrus, right supplementary motor area (SMA) and left precentral gyrus. A weaker functional connectivity was found between the right putamen cluster and the left precentral gyrus in CAI. Greater associations between plantarflexion position sense with cortical activation were observed in the left precentral gyrus, bilateral putamen, and right SMA in CAI, but not in healthy controls.ConclusionsIndividuals with CAI had worse sensorimotor function, experienced lower task-related cortical activation in the sensorimotor network, and had a weaker resting-state functional connectivity between the putamen with the left precentral gyrus compared with healthy controls. Plantarflexion position sense was negatively associated with cortical activation in the left precentral gyrus, bilateral putamen and right SMA in individuals with CAI, but not in healthy controls. These findings suggested that impaired sensorimotor function partly corresponded to potential neurophysiological alterations in individuals with CAI.

Objectives: To compare balance control and ankle proprioception between athletes with and without chronic ankle instability (CAI). A further objective was to explore the relationship between balance control performance and ankle proprioception in athletes with CAI. Design: Cross-sectional study. Settings: Sports Rehabilitation Laboratory. Participants: Eighty-eight recreational athletes (47 CAI and 41 healthy control) were recruited. Interventions: No applicable. Main Outcome Measures: Balance control performance was assessed using the sway velocity of the center of the pressure during the one-leg standing tasks. Ankle proprioception, including joint position sense and force sense, were tested using absolute error (AE) associated with joint position reproduction and force reproduction tasks in 4 directions, that is, plantarflexion, dorsiflexion, inversion, and eversion. Results: Athletes with CAI performed significantly worse than those without CAI in balance control tasks. In addition, CAI athletes showed significantly worse joint position sense and force sense in all 3 movement directions tested (plantarflexion, inversion, and eversion). Correlation analysis showed that the AE of the plantarflexion force sense was significantly moderately correlated with medial-lateral sway velocity in the one-leg standing with eyes open and closed conditions (r=.372-.403, P =.006-.012), and the AE of inversion force sense was significantly moderately correlated with medial-lateral sway velocity in the one-leg standing with eyes open (r=.345, P =.018) in athletes with CAI, but the joint position sense measures were not (all P >0.05). Conclusions: Athletes with CAI showed significantly impaired balance control performance and diminished ankle proprioception. Deficit in force sense was deemed as a moderate predictor of one-leg standing balance control deficits in athletes with dominant-side injury CAI, whereas ankle position sense may be a small predictor. Archives of Physical Medicine and Rehabilitation 2024;105:2127-34 (c) 2024 by the American Congress of Rehabilitation Medicine.

The purpose of this study was to investigate the differences in the morphological and viscoelastic properties of the Achilles tendon (AT) among different groups (rearfoot strikers vs. forefoot strikers vs. non-runners). Thirty healthy men were recruited, including habitual forefoot strike runners (n = 10), rearfoot strike runners (n = 10), and individuals with no running habits (n = 10). The AT morphological properties (cross-sectional area and length) were captured by using an ultrasound device. The real-time ultrasound video of displacement changes at the medial head of the gastrocnemius and the AT junction during maximal voluntary isometric contraction and the plantar flexion moment of the ankle was obtained simultaneously by connecting the ultrasound device and isokinetic dynamometer via an external synchronisation box. The results indicated that male runners who habitually forefoot strike exhibited significantly lower AT hysteresis than male non-runners (p < 0.05). Furthermore, a greater peak AT force during maximal voluntary contraction was observed in forefoot strike male runners compared to that in male individuals with no running habits (p < 0.05). However, foot strike patterns were not related to AT properties in recreational male runners (p > 0.05). The lower AT hysteresis in male FFS runners implied that long-term forefoot strike patterns could enhance male-specific AT’s ability to store and release elastic energy efficiently during running, resulting in a more effective stretch-shortening cycle. The greater peak AT force in male FFS runners indicated a stronger Achilles tendon.

This study aimed to investigate the cortical responses to the ankle force control and the mechanism underlying changes in ankle force control task induced by transcranial direct current stimulation (tDCS). Sixteen young adults were recruited, and they completed the electroencephalogram (EEG) assessment and high-definition tDCS (HD-tDCS) sessions. Root mean square (RMS) error was used to evaluate ankle force control task performance. Spectral power analysis was conducted to extract the average power spectral density (PSD) in the alpha (8-13 Hz) and beta (13-30 Hz) bands for resting state and tasking (i.e. task-PSD). The ankle force control task induced significant decreases in alpha and beta PSDs in the central, left, and right primary sensorimotor cortex (SM1) and beta PSD in the central frontal as compared with the resting state. HD-tDCS significantly decreased the RMS and beta task-PSD in the central frontal and SM1. A significant association between the percent change of RMS and the percent change of beta task-PSD in the central SM1 after HD-tDCS was observed. In conclusion, ankle force control task activated a distributed cortical network mainly including the SM1. HD-tDCS applied over SM1 could enhance ankle force control and modulate the beta-band activity of the sensorimotor cortex.

In recent years, neuro-biomechanical enhancement techniques, such as transcranial direct current stimulation (tDCS), have been widely used to improve human physical performance, including foot biomechanical characteristics. This review aims to summarize research on the effects of tDCS on foot biomechanics and its clinical applications, and further analyze the underlying ergogenic mechanisms of tDCS. This review was performed for relevant papers until July 2023 in the following databases: Web of Science, PubMed, and EBSCO. The findings demonstrated that tDCS can improve foot biomechanical characteristics in healthy adults, including proprioception, muscle strength, reaction time, and joint range of motion. Additionally, tDCS can be effectively applied in the field of foot sports medicine; in particular, it can be combined with functional training to effectively improve foot biomechanical performance in individuals with chronic ankle instability (CAI). The possible mechanism is that tDCS may excite specific task-related neurons and regulate multiple neurons within the system, ultimately affecting foot biomechanical characteristics. However, the efficacy of tDCS applied to rehabilitate common musculoskeletal injuries (e.g., CAI and plantar fasciitis) still needs to be confirmed using a larger sample size. Future research should use multimodal neuroimaging technology to explore the intrinsic ergogenic mechanism of tDCS.

Transcranial direct current stimulation (tDCS) can improve motor control performance under fatigue. However, the influences of tDCS on factors contributing to motor control (e.g., cortical-muscular functional coupling, CMFC) are unclear. This double-blinded and randomized study examined the effects of high-definition tDCS (HD-tDCS) on muscular activities of dorsiflexors and plantarflexors and CMFC when performing ankle dorsi-plantarflexion under fatigue. Twenty-four male adults were randomly assigned to receive five sessions of 20-min HD-tDCS targeting primary motor cortex (M1) or sham stimulation. Three days before and 1 day after the intervention, participants completed ankle dorsi-plantarflexion under fatigue induced by prolonged running exercise. During the task, electroencephalography (EEG) of M1 (e.g., C1, Cz) and surface electromyography (sEMG) of several muscles (e.g., tibialis anterior [TA]) were recorded synchronously. The corticomuscular coherence (CMC), root mean square (RMS) of sEMG, blood lactate, and maximal voluntary isometric contraction (MVC) of ankle dorsiflexors and plantarflexors were obtained. Before stimulation, greater beta- and gamma-band CMC between M1 and TA were significantly associated with greater RMS of TA (r = 0.460-0.619, p = 0.001-0.024). The beta- and gamma-band CMC of C1-TA and Cz-TA, and RMS of TA and MVC torque of dorsiflexors were significantly higher after HD-tDCS than those at pre-intervention in the HD-tDCS group and post-intervention in the control group (p = 0.002-0.046). However, the HD-tDCS-induced changes in CMC and muscle activities were not significantly associated (r = 0.050-0.128, p = 0.693-0.878). HD-tDCS applied over M1 can enhance the muscular activities of ankle dorsiflexion under fatigue and related CMFC.