Ankle sprains are often treated as temporary injuries, but for many people the consequences persist long after swelling and pain have subsided. As many as 70% of individuals who suffer an ankle sprain develop ongoing problems, including impaired balance, reduced proprioception, and difficulty controlling ankle movement. Over time, these deficits can contribute to chronic ankle instability (CAI), a condition in which the ankle repeatedly “gives way” and becomes less reliable during walking, sport, or sudden changes in direction. New research suggests that treating CAI may require more than strengthening muscles and retraining the foot. A study led by researchers at Shanghai University of Sport and Harvard Medical School has found that combining targeted brain stimulation with specialized foot exercises can improve ankle sensory function while also reshaping activity and communication within the brain’s movement networks.
The randomized, double-blind, sham-controlled trial tested an intervention designed to address two components of chronic ankle instability at the same time. One component is peripheral: weakness or impaired coordination in the muscles and sensory systems surrounding the foot and ankle. The other is supraspinal, involving changes in the brain regions responsible for planning, monitoring, and controlling movement. Participants received foot core exercise, a training approach intended to strengthen the small intrinsic muscles of the foot and improve sensorimotor control. At the same time, some participants received individualized high-definition transcranial direct-current stimulation, or HD-tDCS, while a control group underwent sham stimulation. The program consisted of 20-minute sessions three times a week for four weeks.
The study, led by Professor Weijie Fu of the School of Intelligent Sports Engineering at Shanghai University of Sport in China and Professor Junhong Zhou of Harvard Medical School in the United States, involved 34 people with chronic ankle instability. Researchers assessed participants before and after the intervention using task-related functional magnetic resonance imaging and ankle force-sense measurements. Force sense refers to the ability to accurately judge how much force is being produced during a movement, even without relying on vision. This capacity is essential for maintaining balance, adjusting foot placement, and preventing excessive or poorly controlled ankle motion. Participants were tested on their ability to sense forces during dorsiflexion, inversion, and eversion—the upward, inward, and outward movements of the ankle and foot.
Unlike conventional transcranial direct-current stimulation protocols, which often use standardized electrode positions based on the EEG 10/20 system, the researchers used an individualized dose-controlled approach. Standard electrode arrangements can produce different electric-field patterns from one person to another because skull thickness, brain shape, tissue conductivity, and the location of functional brain regions vary across individuals. In this study, each participant’s brain structure was used to optimize the electrode montage and current distribution. HD-tDCS uses a configuration of small electrodes to deliver a more spatially focused electrical stimulus than traditional two-electrode tDCS. The aim was to maximize current flow in a selected sensorimotor region while limiting unintended stimulation of nearby areas.
The intervention produced measurable changes in brain activity during ankle motor tasks. Compared with the sham-stimulation group, participants who received individualized HD-tDCS alongside foot core exercise showed reduced task-related activation in both inferior parietal lobules and in the right supplementary motor area. These regions form part of a broader network involved in integrating sensory information, representing body position, planning movement, and monitoring actions. Reduced activation does not necessarily indicate diminished brain function. In the context of motor control, it may reflect more efficient processing, meaning that the brain can perform the same task with less neural effort after training. The finding is particularly notable because earlier studies had linked chronic ankle instability with altered cortical responses during dorsiflexion and plantarflexion tasks.
The researchers also observed stronger functional connectivity between the left inferior parietal lobule and the right putamen. Functional connectivity measures the degree to which activity in separate brain regions fluctuates in a coordinated manner, even when the regions are not directly connected by a single anatomical pathway. The putamen, a structure within the basal ganglia, contributes to movement selection, motor learning, and the refinement of practiced actions. Communication between parietal regions and the putamen may help the brain combine sensory information about the foot with the motor commands needed to stabilize the ankle. Enhanced connectivity therefore suggests that the intervention may have improved coordination between sensory interpretation and movement regulation.
These changes in brain organization were accompanied by improvements in ankle force sense. Participants receiving the combined intervention demonstrated better awareness of dorsiflexion, inversion, and eversion forces after four weeks of training. The study also reported relationships between changes in sensory performance and changes in brain measurements. Improvements in force sense were negatively correlated with signal-intensity changes in the right inferior parietal lobule and right supplementary motor area, indicating that reductions in task-related activation were associated with better sensory accuracy. Changes in force sense were also marginally associated with increased connectivity between the left inferior parietal lobule and right putamen. Together, the findings suggest that improved ankle function may be linked not only to stronger muscles or more responsive peripheral receptors, but also to more efficient central processing.
Foot core exercise has traditionally been used to address local impairments in CAI, including weakness, poor balance, and reduced proprioception. Transcranial stimulation, by contrast, is intended to influence cortical excitability and the brain’s capacity to adapt during training. Combining the two approaches may create a form of coordinated rehabilitation in which the peripheral system supplies richer sensory information while the brain becomes better able to interpret and use it. The stimulation was delivered concurrently with exercise, a timing strategy that may be important because the brain is more likely to reorganize when neuromodulation is paired with active, meaningful movement. Rather than attempting to replace physical rehabilitation, the approach is designed to amplify the neural effects of functional practice.
The researchers caution that the trial represents an early stage in evaluating multimodal treatment for chronic ankle instability. The sample was small, the intervention lasted only four weeks, and the outcomes were measured shortly after training. Further research will be needed to determine whether the improvements persist, whether they translate into fewer recurrent ankle sprains and better performance during sport, and which patients are most likely to benefit. Larger studies could also clarify the optimal stimulation dose, electrode configuration, exercise progression, and treatment duration. Nevertheless, the results provide evidence that CAI involves modifiable changes across both peripheral and central systems. By combining individualized neuromodulation with targeted exercise, rehabilitation may eventually be tailored to the unique anatomy and neural profile of each patient.
“We concluded that a four-week intervention of individualized dose-controlled HD-tDCS combined with foot core exercise effectively reduced cortical activation during ankle motor tasks, strengthened functional connectivity within relevant supraspinal networks, and enhanced sensorimotor function in individuals with chronic ankle instability,” Professor Fu said. The findings support a broader shift in rehabilitation science toward multi-target interventions that treat the nervous system as an integrated whole. For people whose ankles remain unstable long after an initial sprain, the most effective therapy may not focus exclusively on the injured joint. It may also retrain the brain’s maps, networks, and predictions of how the foot should move.
Subject of Research: People with chronic ankle instability
Article Title: Functional characteristics in supraspinal networks and sensorimotor function following individualized dose-controlled HD-tDCS during foot core exercise in chronic ankle instability
News Publication Date: 29-May-2026
Web References: https://doi.org/10.1016/j.jshs.2026.101148
References: Journal of Sport and Health Science; DOI: 10.1016/j.jshs.2026.101148
Image Credits: Professor Weijie Fu, Shanghai University of Sport, China, and Professor Junhong Zhou, Harvard Medical School, USA
Keywords: chronic ankle instability, ankle sprain, HD-tDCS, transcranial direct-current stimulation, foot core exercise, sensorimotor function, functional connectivity, functional magnetic resonance imaging, brain stimulation, rehabilitation, proprioception, ankle force sense
Tags: ankle sprain long-term effectsbrain stimulation for ankle rehabchronic ankle instability treatmentfoot muscle strengthening exercisesinnovative interventions for chronic ankle instabilitymulti-target approach to ankle instabilityneural communication in movement networksneural plasticity in movement controlproprioception recovery in ankle injuriesrandomized controlled trial for ankle treatmentsensory-motor integration in ankle rehabsupraspinal contribution to ankle stability
