Context: Although neuromuscular deficits in people with chronic ankle instability (CAI) have been identified, previous studies mostly investigated the activation of multiple muscles in isolation. Investigating muscle synergies in people with CAI would provide information about the coordination and control of neuromuscular activation strategies and could hold important information for understanding and rehabilitating neuromuscular deficits in this population.

Objective: The purpose of this study was to investigate muscle synergies in people with CAI and healthy controls as they perform different cutting tasks.

Design: Cross-sectional study

Setting: Laboratory

Participants: Eleven people with CAI (22 ± 3 years, 1.68 ± 0.11 m, 69.0 ± 19.1 kg) and 11 healthy controls (CON) (23 ± 4 years, 1.74 ± 0.11 m, 66.8 ± 15.5 kg) participated in the current study.

Main Outcome Measures: Muscle synergies were extracted from the EMG of the soleus, medial gastrocnemius, lateral gastrocnemius, tibialis anterior, and fibularis longus muscles during anticipated and unanticipated cutting tasks. The number of synergies, activation coefficients, and muscle-specific weighting coefficients were compared between groups and across tasks.

Results: The number of muscle synergies were the same for each group and task. The CAI group exhibited significantly greater (p = 0.023) tibialis anterior weighting coefficients within Synergy 1 compared to the CON group. In addition, both groups exhibited greater fibularis longus (p = 0.029) weighting coefficients within Synergy 2 during unanticipated cutting compared to anticipated cutting.

Conclusion: These results suggest that while both groups used a neuromuscular control strategy of similar complexity / dimensionality to perform the cutting tasks, people with CAI exhibited different muscle-specific weightings characterized by greater emphasis on tibialis anterior function within Synergy 1, which may reflect an effort to increase joint stability to compensate for the presence of ankle instability.

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