The investigation of nonlinear variability underlying postural control in the injure-limb in individuals with and without chronic ankle instability

Background: Less flexible and adaptable sensorimotor systems associated with Chronic Ankle Instability (CAI) limit the detection of relevant sensory feedback information, resulting in decreased movement variability. Consequently, when faced with challenging environmental constraints, particularly with conditions that manipulate sensory feedback, individuals with CAI may become more prone to repetitive ankle sprains. This study aimed to investigate the neural control underlying postural control in the injured-limb during increased environmental constraints with sensory feedback manipulations in individuals with and without CAI, respectively. Methods: Forty-two individuals with and without CAI participated in the study and completed the sensory organization test (SOT). The SOT assesses the ability to integrate primary sensory feedback across six conditions that manipulate somatosensory and visual feedback with a combination of a sway-referenced support surface and visual surroundings. The nonlinear method of sample entropy (SampEN) was used to quantify the neural control underlying postural control. A one-way ANOVA examined group differences in neural control during the SOT conditions while standing on the injured-limb. Results: Individuals with CAI demonstrated significantly lower SampEN while maintaining posture in conditions where they were forced to rely exclusively on vestibular feedback in the injured-limb compared to healthy controls (P < 0.05). Conclusions: Individuals with CAI did not demonstrate decreased movement variability (neural control) in most of the six SOT conditions. However, the CAI group exhibited decreased movement variability, specifically when they had to rely on vestibular feedback while maintaining posture in the injured-limb compared to healthy controls. Future studies should investigate how manipulation of vestibular feedback affects movement variability with gait in individuals with CAI.