Muscle synergies of lower extremity during gait initiation in individuals with and without chronic ankle instability

Abstract

Title:Muscle synergies of lower extremity during gait initiation in individuals with and without chronic ankle instability Objective:Chronic ankle instability (CAI), which occurs following an acute ankle sprain. Gait initiation (GI) is the safest task to disrupt postural stability and evaluate its result,which has a specific pattern in the CNS. Specific patterns associated with the central nervous system can be evaluated through analysis of muscle synergy. Muscle synergy refers to coordinated activations of groups of muscles. The aim of this study is to investigate muscle synergies of lower extremity during gait initiation in individuals with and without CAI. Method:Twenty participants,10 per group, volunteered to participate. The subjects initiate gait upon hearing the auditory cue while standing on the force plate. The kinematic and kinetic data extracted by NEXUS software and used for simulating the musculoskeletal model in OpenSim software. Muscle synergy was calculated using HALS method by a custom program written in MATLAB software.The dependent variables were analyzed using Wilcoxon and one-way analysis of variance (ANOVA) tests by use of the SPSS software. Results:The results showed no significant difference in the number of synergies between two groups (P>0.05). However, there were significant differences in muscle weightings for synergy 1 and 2 between the two groups (P<0.05). Specifically, within Synergy 1, the weighting of the Tibialis Anterior (TA) muscle and within Synergy 2, the weighting of the Rectus Femoris (RF) and Gluteus Maximus_left (GM_L) muscles were greater for the CAI group than control group.Also, within Synergy 3, weighting of the Peroneus Longus (PL) muscle was greater for the control group than CAI group. Conclusion:It seems the inhibition of PL muscle is compensated by hyperactivity TA, RF, and GM_L muscles in those with CAI. This interaction and compensation in the movement strategy can be considered as Ankle strategy in GI.The results suggest that the motor chain is disrupted and the complexity is increased. So, this impairment is not local musculoskeletal condition. In general, in individuals with chronic ankle instability or any musculoskeletal disorder that has become chronic, the neuromuscular activation patterns of CNS are altered. Therefore, CAI is as a global condition.