Ankle Nerve Signals Reveal Hidden Timing Errors in Unstable Ankles

Chronic ankle instability is one of the most common consequences of a seemingly minor injury. After a first ankle sprain, a substantial fraction of people go on to develop repeated episodes of the joint ‘giving way’, persistent feelings of instability, and long-term functional limitations that can persist for decades. For years, clinicians have suspected that part of the problem lies not in the damaged ligaments themselves but in the sensory feedback those ligaments once provided. Now, a new modeling study published in Scientific Reports offers one of the most detailed pictures yet of how the timing of proprioceptive nerve signals from the ankle is disrupted at the precise moment it matters most: the instant we begin to walk.

Gait initiation is a deceptively complex act. The nervous system must shift the body’s center of mass forward and toward the swing limb, unweight the trailing leg, and generate carefully sequenced bursts of muscle activity, all within a few hundred milliseconds. During this window, sensory receptors embedded in muscles, tendons, joints, and skin fire continuously, informing the central nervous system about joint position, movement velocity, and load. Researchers have long measured how quickly muscles respond to perturbations in people with chronic ankle instability, but far less attention has been paid to the afferent side of the circuit — the incoming stream of proprioceptive signals that arrives before any muscle can react. Because direct recordings of these nerve signals in humans are ethically and technically impractical, the research team turned to a computational approach.

The study combined detailed biomechanical analysis of gait initiation with a neurophysiological model of proprioceptor behavior. Participants, including individuals with chronic ankle instability and healthy controls, walked in a motion capture laboratory equipped with force plates that recorded the ground reaction forces beneath each foot. From the movement trajectories and forces, the researchers reconstructed the mechanical events inside and around the ankle joint: changes in joint angle, angular velocity, muscle fascicle length, and the deformation of skin and joint capsules. These mechanical variables were then fed into mathematical models describing how different classes of proprioceptive afferents translate mechanical deformation into trains of neural impulses.

The models captured the behavior of several key sensory populations. Muscle spindles, the primary detectors of muscle length and stretch velocity, were modeled with their characteristic dynamic and static response components. Golgi tendon organs, which signal tensile load within tendons, were modeled as force-sensitive elements. Cutaneous and joint mechanoreceptors, which fire in response to skin stretch and joint capsule deformation, were included as well. Each model produced an estimate of instantaneous firing rate — effectively, a simulated neurogram of what the ankle’s sensory apparatus was telling the spinal cord and brain at every millisecond of the gait initiation sequence.

The central finding is striking: in individuals with chronic ankle instability, the estimated timing of proprioceptive afferent activity was systematically altered during the anticipatory postural phase of gait initiation. Whereas healthy participants showed well-organized, temporally structured afferent volleys that preceded and accompanied the postural adjustments needed to step forward, the unstable ankles displayed shifts and distortions in these signal patterns. In practical terms, the sensory information reaching the nervous system about the ankle’s position and loading arrived in a different temporal pattern than in uninjured joints. Because the nervous system depends on precisely timed sensory feedback to calibrate motor commands, even modest shifts in afferent timing could degrade the coordination of the postural adjustments that keep the body balanced during the transition to stepping.

The researchers emphasize that the disruption is not simply a matter of weaker signals. The models suggested changes in the relative timing between different receptor populations, meaning that the brain may receive internally inconsistent information about what the ankle is doing. Muscle spindle signals indicating one joint position may arrive in a different relationship to cutaneous signals than the nervous system has learned to expect. This form of sensory reweighting or desynchronization is thought to be a hallmark of the maladaptations that follow ligament injury, when damaged mechanoreceptors in the torn ligament are lost and remaining receptors must compensate — often imperfectly — for the missing input.

What makes this approach particularly powerful is that it opens a window onto a process that has been essentially invisible in human experiments. Traditional assessments of proprioception in chronic ankle instability, such as joint position matching tasks or thresholds for detecting passive movement, measure perception at one static moment in time. They cannot capture the rapid, continuous stream of sensory traffic that flows during movement. By deriving afferent firing patterns from movement data through validated receptor models, the study provides a dynamic, millisecond-by-millisecond estimate of sensory signaling during a functional task. This is a fundamentally different lens from reactive measures such as reaction times or postural sway scores, which reflect the end result of sensory-motor integration rather than its incoming raw material.

The clinical implications are potentially significant. Rehabilitation programs for chronic ankle instability currently emphasize balance training, strengthening, and perturbation-based exercises, which are effective for many but not all patients. If the root of the problem lies in altered afferent timing during the anticipatory phase of movement, then therapies could be designed specifically to recalibrate sensory signaling. Tasks that demand precise ankle positioning under time pressure, or training environments that manipulate the relationship between movement and sensory feedback, might encourage the nervous system to relearn the temporal patterns it lost after injury. The modeling framework also suggests new outcome measures: instead of relying solely on questionnaires and postural tests, clinicians could one day track afferent timing metrics derived from inexpensive motion capture to quantify sensory recovery objectively.

The study also fits into a broader scientific movement that treats sensory timing as a central currency of motor control. Research across domains, from upper limb reaching to locomotion in older adults, has shown that the nervous system is exquisitely sensitive to delays and variability in sensory feedback. Even artificial delays of tens of milliseconds can disrupt motor learning and adaptation. In this light, chronic ankle instability can be understood not merely as a mechanical joint problem or a strength deficit, but as a disorder of sensorimotor timing — a failure of the dialogue between the ankle and the spinal cord to keep the conversation synchronized during the most demanding phases of movement.

There are, of course, important caveats. The afferent patterns in this study are model-derived estimates, not direct neural recordings, and their accuracy depends on the fidelity of the underlying neurophysiological models and the biomechanical reconstructions. Individual variability in anatomy, injury history, and compensation strategies means that the group-level patterns reported here may not apply uniformly to every patient. The researchers also note that gait initiation, while clinically relevant, is only one of many tasks in which altered afferent timing could play a role; landing, cutting, and uneven-terrain walking may each impose distinct sensory demands. Future work combining these modeling techniques with other modalities, such as electroencephalography or high-density electromyography, could trace how altered afferent timing propagates through the central nervous system to produce the characteristic motor deficits of the condition.

Nevertheless, the study marks an important step toward a mechanistic, quantitative understanding of one of sports medicine’s most stubborn problems. By converting observable movement into estimated neural signaling, it transforms chronic ankle instability from a fuzzy clinical label into a measurable pattern of sensory disruption with specific temporal signatures. If subsequent studies confirm and extend these findings, the humble ankle sprain — so often dismissed as a trivial injury — may finally be understood at the level of the nerve impulses it deranges, and treated accordingly.

Subject of Research: Model-derived proprioceptive afferent timing during gait initiation in chronic ankle instability

Article Title: Model-derived proprioceptive afferent timing during gait initiation in chronic ankle instability

Article References: Bijari, K., Sadeghi, H., Yousefi, M., & Yiou, E. (2026). Model-derived proprioceptive afferent timing during gait initiation in chronic ankle instability. Scientific Reports. https://doi.org/10.1038/s41598-026-71074-4

Image Credits: AI Generated

DOI: 10.1038/s41598-026-71074-4

Keywords: chronic ankle instability, proprioception, gait initiation, afferent timing, muscle spindles, Golgi tendon organs, sensorimotor control, computational modeling, biomechanics, ankle sprain, postural control, neurogram