| Abstract ID |
| 20260032 |
| Category |
| Foot & Ankle |
| Preferable Presentation |
| Oral Presentation |
| Title |
| ALTERED FEEDFORWARD AND FEEDBACK CO-CONTRACTION IN CHRONIC ANKLE INSTABILITY DURING UNEXPECTED WALKING PERTURBATIONS |
| Author |
|
| Presenter |
| wenqi ran |
| Abstract |
| Background Lateral ankle sprains (LAS) account for approximately 90% of ankle injuries, with up to 40% of cases progressing to Chronic Ankle Instability (CAI), a condition characterized by recurrent sprains and sensorimotor deficits. During gait, functional stability relies heavily on muscle co-contraction to modulate dynamic joint stiffness. Since the latency of muscular reflex often exceeds the time required for an inversion injury to occur, adequate preparatory and reactive stiffness is the primary mechanical defense against excessive displacement. However, this regulation may be compromised in individuals with CAI due to proprioceptive deficits and altered neuromuscular control. Previous research has largely prioritized static or anticipated tasks, leaving stiffness modulation poorly understood during unexpected walking perturbations, which is the scenario most relevant to injury recurrence in individuals with CAI. Objectives This study aimed to investigate continuous ankle muscle co-contraction patterns in individuals with CAI during unexpected walking perturbations using Statistical Parametric Mapping (SPM), thereby elucidating the neuromuscular mechanisms underlying recurrent instability. Study design Forty participants, comprising twenty individuals with CAI and twenty age- and gender-matched controls, were recruited. The study was approved by the Ethics Committee of Shandong Sport University (Approval No. 2025053). Participants walked at a self-selected speed on a custom-built walkway featuring a trapdoor capable of inducing a sudden 24° inversion perturbation to simulate the mechanism of a lateral ankle sprain. To ensure unpredictability, perturbations were triggered randomly (6 perturbation trials out of 10), and trials involving anticipation were excluded. Surface EMG signals from the Tibialis Anterior (TA), Peroneus Longus (PL), and Soleus (SOL) were recorded, processed via standard filtering and normalization procedures, and time-normalized for analysis (±200 ms relative to perturbation). Dynamic joint stiffness was quantified using the Rudolph Co-contraction Index (CCI) for the frontal and sagittal planes based on the average of three successful non-anticipated trials. SPM independent t-tests were conducted to identify significant differences in continuous CCI waveforms (α = 0.05). Results No significant between-group differences were observed for demographic characteristics (P > 0.05). In the frontal plane (TA/PL), SPM analysis revealed a distinct biphasic shift: compared to controls, individuals with CAI exhibited significantly higher CCI during the pre-perturbation phase (-69 to 4 ms; P = 0.014), followed by significantly lower CCI during the post-perturbation phase (76 to 101 ms; P = 0.020). No significant differences were found in the sagittal plane (TA/SOL) (P > 0.05). Conclusions The observed biphasic shift reflects a dissociated neuromuscular strategy in CAI. While elevated pre-activation suggests compensatory feedforward stiffening, the subsequent feedback deficit occurs during the critical loading phase, limiting the joint's ability to resist inversion forces. This failure to sustain reactive co-contraction compromises medial-lateral stability, directly predisposing the joint to recurrent sprains. |