# Exposure to visual perturbations elicits adaptation in step kinematics during gait in those with chronic ankle instability

## TL;DR

People with chronic ankle instability show changes in walking patterns when exposed to visual disruptions, suggesting sensorimotor control issues.

## Contribution

The study reveals time-dependent adaptations in step kinematics and variability in response to visual perturbations in individuals with chronic ankle instability.

## Key findings

- Early adaptation to visual perturbations increased step width and variability while decreasing step length.
- Late adaptation showed contrasting changes in step length and width depending on the type of visual perturbation.
- Post-test results indicated reduced step width and increased variability after exposure to visual disruptions.

## Abstract

Chronic ankle instability (CAI) is associated with impaired gait adaptability, and investigating time-dependent changes in step kinematics and variability—particularly step-to-step corrections—under visually-disruptive conditions compared to a control setting may offer valuable insights into the sensorimotor deficits underlying this condition.

This cross-over investigation included nineteen participants (Age: 22±3 years, 5±3 sprains, 7±9 giving-way episodes, 23±6 IdFAI score). Inclusion criteria followed International Ankle Consortium guidelines. Participants completed two 15 min walking trials on an instrumented treadmill at 1.2 m/s surrounded by a speed-matched virtual hallway. Within each 15-minute assessment, participants walked normally without visual perturbations for the first (Pre-test) and last two minutes (Post-test). Between these assessments, participants were exposed to 10 min of either continuous mediolateral optical flow perturbations (OFP) or stroboscopic vision (SV) and a 1-minute active rest period. This window allowed us to capture early (first two minutes of exposure) and late (last two minutes of exposure) adaptation. Means and standard deviations of step widths (SW), step lengths (SL), and their respective variabilities (SWV, SLV) were calculated from consecutive heel positions. For each visual condition, separate repeated measures ANOVA were used.

We observed significant changes over time for both OFP and SV (p ≤ 0.036). In early adaptation, for both OFP and SV, SL decreased, while SW and SWV increased (p ≤ 0.009). In late adaptation for OFP, SL increased (p = 0.012) while SLV decreased (p = 0.002). During the same period for SV, SW decreased (p = 0.002) while SL (p = 0.008) increased. Post-test demonstrated reduced SW (p ≤ 0.036) and increased SWV (p ≤ 0.022) relative to Pre-test for OFP and SV.

This study identified time-dependent changes in step kinematics and variability in response to OFP and SV among individuals with CAI. The observed changes indicate a reduction in anticipatory control and an increase in reactive control with prolonged exposure to visual perturbations. A short-term aftereffect of the step-to-step reactive control strategy was also observed.

The online version contains supplementary material available at 10.1186/s12984-025-01705-w.