Reduced Effective Postural Responses to External Perturbations in Chronic Ankle Instability.

Chronic ankle instability (CAI) is associated with postural control deficits due to altered postural strategy, particularly during transitions between postures (e.g., landing followed by immediate medial jump) and in response to sudden external perturbations. However, postural stability and the underpinning joint action remain unclear. This study aimed to identify differences in postural response to a mediolateral moving platform during single-leg stance between individuals with CAI and healthy controls (HC). Twenty-three CAI and 23 HC participants performed balance tasks during 1-s mediolateral perturbation. Ground reaction force and kinematic data were recorded, and margin of stability (MoS), and joint torques in the frontal plane were calculated for their first successful trial. The CAI group showed increased MoS during sudden changes in platform movement direction (p = 0.045) and the phase after platform stop (p = 0.033) compared to the HC, suggesting a less effective postural response to external perturbations. These findings suggest a less stable postural strategy in people with CAI during single-leg stance with perturbation. The weaker relationship between MoS and hip- and trunk- torque in the CAI than HC group in response to the perturbation provided evidence for reduced effectiveness of joint actions in postural control. Sudden base of support changes, such as accelerations and decelerations, are shown to be effective in identifying postural impairments in CAI. Further research is needed to determine whether these impairments can be improved through practice.