Muscle Synergies in People With Chronic Ankle Instability During Anticipated and Unanticipated Landing-Cutting Tasks

Abstract

Context: Although neuromuscular deficits in people with chronic ankle instability (CAI) have been identified, previous researchers have 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 supply important information for understanding and rehabilitating neuromuscular deficits in this population. Objective: To assess and compare muscle synergies using nonnegative matrix factorization in people with CAI and healthy control individuals as they performed different landing-cutting tasks. Design: Cross-sectional study. Setting: Laboratory. Patients or Other Participants: A total of 11 people with CAI (5 men, 6 women; age = 22 +/- 3 years, height = 1.68 +/- 0.11 m, mass = 69.0 +/- 19.1 kg) and 11 people without CAI serving as a healthy control group (5 men, 6 women; age = 23 +/- 4 years, height = 1.74 +/- 0.11 m, mass = 66.8 +/- 15.5 kg) participated. Main Outcome Measure(s): Muscle synergies were ex-tracted from electromyography of the lateral gastrocnemius, medial gastrocnemius, fibularis longus, soleus, and tibialis anterior (TA) muscles during anticipated and unanticipated landing-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 was the same for each group and task. The CAI group exhibited greater TA weighting coefficients in synergy 1 than the control group (P = .02). In addition, both groups demonstrated greater fibularis longus (P = .03) weighting coefficients in synergy 2 during the unanticipated landing-cutting task than the anticipated landing -cutting task. Conclusions: These results suggest that, although both groups used neuromuscular control strategies of similar complexity or dimensionality to perform the landing-cutting tasks, the CAI group displayed different muscle-specific weight-ings characterized by greater emphasis on TA function in synergy 1, which may reflect an effort to increase joint stability to compensate for ankle instability.