Anticipation may underestimate neuromechanical deficits in chronic ankle instability during walking inversion...

This study aimed to compare ankle kinematics and lower limb muscle activation between individuals with and without chronic ankle instability (CAI), both prior to and following an inversion perturbation during walking, with a particular focus on how anticipation modulates muscle activation and the consequent ankle inversion post-perturbation.

Forty-six participants were enrolled, including 23 with CAI and 23 age- and sex-matched non-CAI controls. They walked at a self-selected pace on a custom-designed platform equipped with a trapdoor programmed to trigger a 24° inversion perturbation under both anticipated and unanticipated conditions. Ankle kinematics and lower limb muscle electromyography were synchronously collected during a 400-ms window, specifically 200 ms pre- and 200 ms post-perturbation. Continuous time-series data were compared using a two-way mixed-design ANOVA via Statistical Parametric Mapping.

Significant interactions were detected in ankle inversion angles (30.0-105.0 ms, F _max = 29.981, = 8.337, p = 0.005), as well as for the activation of the peroneus longus (PL) (67-121 ms, F _max = 25.097, p = 0.005) and pre-activation of lateral gastrocnemius (LG) (-200 to -161 ms, F _max = 15.694, p = 0.014). Transitioning from anticipated to unanticipated conditions elicited an increase in ankle inversion across both individuals with and without CAI, with a significantly greater magnitude of increase observed in CAI individuals (all p < 0.001). Individuals without CAI significantly increased their PL activation when transitioning from anticipated to unanticipated conditions (p < 0.001), whereas the CAI individuals exhibited no significant change. Conversely, individuals with CAI demonstrated a significant increase in LG pre-activation (p = 0.006), while those without CAI exhibited no significant change.

Under unanticipated perturbations, the compensatory increase in LG pre-activation observed in individuals with CAI remains insufficient to offset diminished PL activation and the subsequent increase in ankle inversion. These neuromechanical deficits, typically masked by anticipation, indicate that predictable paradigms may not fully capture real-world injury scenarios. Rehabilitation should prioritize targeted PL recruitment to enhance dynamic stability and reduce reinjury risk.