Ankle sprain is the most prevalent sports-related injury affecting the lower limbs, and up to 70% of individuals with ankle sprain experience persistent symptoms, such as sensorimotor impairment and balance deficits, which may ultimately progress to chronic ankle instability (CAI). In addition to peripheral neuromuscular alterations, impaired sensorimotor function in individuals with CAI has been linked to functional changes within supraspinal regions. For instance, authors and others have demonstrated that individuals with CAI exhibit reduced cortical activation in response to dorsi-plantarflexion tasks and diminished resting-state functional connectivity (FC) within the sensorimotor network, as measured by functional magnetic resonance imaging (fMRI), when compared to healthy controls.
Traditionally, interventions for CAI, such as foot core exercise (FCE), mainly focus on peripheral dysfunctions. Previous studies have demonstrated that FCE can improve a range of functional impairments in individuals with CAI, including balance control, muscle strength, and proprioception. Meanwhile, efforts have been devoted to exploring the effects of strategies targeting supraspinal elements on sensorimotor function in CAI. One such approach is transcranial direct current stimulation (tDCS), which is a noninvasive neuromodulation technique for modulating cortical excitability in sensorimotor regions. Evidence suggests that tDCS can improve sensorimotor function and balance control in individuals with CAI. In a pilot study, the authors were the first to investigate the effects of a 4-week intervention combining FCE with high-definition tDCS (HD-tDCS) to simultaneously target peripheral and supraspinal components in a cohort of healthy young adults. The combined intervention produced considerably greater improvements in toe flexor strength and foot–ankle sensory function than with FCE alone. These findings suggest that "multi-target" interventions may yield superior therapeutic outcomes in CAI compared to conventional, single-target approaches. However, the effects of such multimodal interventions on the functional characteristics of supraspinal networks in individuals with CAI remain largely unexplored.
A new study led by Professor Weijie Fu from the School of Intelligent Sports Engineering, Shanghai University of Sport, China, along with Professor Junhong Zhou from Harvard Medical School, USA, conducted a randomized, double-blind, and sham-controlled trial to investigate the effects of a multimodal intervention, combining HD-tDCS and FCE, on supraspinal functional characteristics and sensorimotor function in individuals with CAI. "Recognizing that template-based tDCS montages (e.g., those based on the electroencephalogram (EEG) 10/20 system) often result in substantial variability in electric field distribution due to inter-individual differences in brain anatomy, we employed an individualized tDCS protocol," says Prof. Fu. This protocol optimized electrode montage on the basis of each participant's brain structure, with the goal of maximizing current flow within the targeted sensorimotor region. The study was made available online on May 29, 2026, and will be published in Journal of Sport and Health Science on December 1, 2026.
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. Participants received 20 minutes 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.
The study found that 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 FC between the left inferior parietal lobule and the right putamen. Additionally, improved dorsiflexion, inversion, and eversion force senses were observed. Moreover, changes in force sense were negatively correlated with changes in signal intensities in the right inferior parietal lobule and rSMA, and were marginally significantly associated with changes in FC between the left inferior parietal lobule and right putamen.
"We concluded that 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," says Prof. Fu, the study's lead author. He adds "These findings support the potential of individualized neuromodulation combined with functional training as a promising strategy to restore ankle sensorimotor function through central mechanisms."
