Introduction: Delayed neuromuscular responses is the most important lesions in individuals with functional ankle instability (FAI) indicating of using the compensatory mechanisms. Since the most movements occurred in closed- kinetic chain, the distal lesions effect on the proximal sections and cause to use the compensatory strategies. The aim of this research was to study the compensatory strategies during gait in individual with functional ankle instability by use of inversion perturbation.
Methodology: 7 healthy subjects (age 23.40±1.70 years; weight 72.25±6.14 Kg; height 176.32±6.41 cm) and 7 individuals with functional ankle instability (age 24.31±0.81 years; weight 71.15±7.21 Kg; height 175.12±4.28 cm) participated voluntarily in the semi-experimental research. Electrical activation of the peroneus longus, tibialis anterior, gluteus medius, and erector spine muscles during gait on the inversion perturbation system has been measured using the wireless EMG system (MYON Company; Switzerland). Response time to perturbation (RTP) in electrical signals of the muscles has been extracted with the custom program on MATLAB software and analyzed by use of the independent T-test (p<0.05).
Results: FAI group as compare with the healthy group indicated the significant longer RTP in the peroneus longus and erector spine muscles (p<0.05), whereas RTP in gluteus medius muscle was significantly lesser in FAI group (p<0.05). Although, RTP in tibialis anterior muscle was longer in FAI group as compare with the healthy group, there was not any significant difference between two groups.
Discussion: The results of this study showed that RTP in FAI group differ from the healthy group. Sooner recruitment of gluteus medius muscle in FAI group is indicator of using the hip-based strategy to control posture. Since the FAI individuals have lesions in muscle surrounding the ankle, so ankle-based strategy is not enough to response the perturbation, for this reason the dominant strategy for controlling the posture is hip – based strategy. Alterations in RTP reports owing to variation of the central neuromuscular control, so proposed to practitioner to focus on detecting the inefficiency compensatory mechanism.