Study Of The Neuromuscular Control Of The Ankle Joint With Functional Instability

Objectives: Ankle sprain can lead to a chronic condition called functional ankle instability(FAI). The reason of ankle sprain recurrently was unknown. The purpose of this study was to investigate the proprioception, biomechanics of the maximal concentric and eccentric contraction, and the effects of repeated maximal concentric exercise on the proprioception and biomechanics of the ankle joint with functional ankle instability(FAI), in order to explore the neuromuscular control of the ankle joint and the effects of fatigue on them ,and to provide theoretical and experimental reference for the solid understanding of FAI group in the the clinic and rehabilitation training.Methods: The ankles of 28 college-aged males were tested in this study. Fourteen of the subjects had unilateral FAI, while the other 14 subjects were matched-paired and served as controls. The CON-TREX isokinetic dynamometer and the biovision system were synchronously used to collect peak torque, SEMG of the muscles and the angle of the joint. The target angle of the ankle passively reposition was 5°of plantar flexion to measure joint position sense(JPS). The target force of the muscle was 25% maximal voluntary isometric contraction to measure the muscle force sense(MFS). A multivariate repeated measures ANOVA was used to determine time-dependent differences, and the differences before and after fatigue in neuromuscular control between the two groups with FI and without FI, between different velocities(60 and 180°? s?1). Dependent variables were the characters of proprioception and biomechanics. T test was used to determine the cycles'differences until maximal concentric fatigue between the two groups with FI and without FI. Product-moment correlation analysis was used to determine the relationship between proprioception and biomechanics of ankles. Results : (1)Interclass correlation coefficients(ICC) of variable errors(VE) and absolute errors(AE) in JPS and MFS were more than 0.75, and standard errors of measurement(SEM) of them were less. ICCs of constant error(CE) of them are less than 0.75, and SEMs of them are greater. (2)There were significant differences between the two groups with and without FI, and the difference was not in JPS and relative peak torque of dorsal flexion(P >0.05)but in MFS, relative peak torque of plantar flexion, and dynamic control rate(DCR)(P <0.05). (3) There is no significant difference under the different velocity (P >0.05). The higher the velocity was, the higher the rate of eccentric peak torque to concentric peak torque. (4)No significant correlation was found between JPS and the biomechanical characters(P >0.05). Significant, but low and medium correlation was found between the two groups for MFS and some of the torque characters. (5) For either group, there was a significant main effect for JPS and MFS across both fatigue method(P >0.05), but the effect of concentric exercise was greater than that of eccentric exercise. (6) Coefficient of variation(CV),of the instantaneous median frequency based on wavelet time-frequency analysis for SEMG,was lower than that of median frequency(MF) and mean power frequency(MPF) based on FFT. (7) Tibialis anterior for the group with FI was easier to get fatigue than that for the group without FI. (8) MPF and IMDF, of TA and medial head of gastrocnemius muscle for the group with FI, are time-dependent. But for the group without FI,the indexes of SEMG were time-independent.Conclusions:(1) The test-retest reliability for VE and AE of JPS and MFS was better than CE of them. (2) Compared to group without FI, MFS and muscular strength were impaired in plantar flexion of the ankle for the group with FI. During the maximal isokinetic concentric fatigue, Tibialis anterior muscle was easier to get fatigue. Soleus and the lateral head of gastrocnemius may exist in arthrogenous muscle inhibition. The plantarflexor may have been destroyed after ankle sprain, thus, the recruitment of motor unit of muscle is changed. (3)There was no difference, for JPS, and the concentric and eccentric peak torque of the dorsiflexor, between the two groups with and without FI. (4)There was no linear correlation between JPS and the biomechanical characters of the ankle, and the correlation was low and medium between MFS and the biomechanical characters of the ankle joint. (5) Dynamic control rate (DCR)of muscle may be one of the evaluation indexes of ankle functional stability. (6)Proprioception after local muscle fatigue was worse than before for either fatigue method, and the influence from maximal isokinetic concentric fatigue was greater than that from maximal isokinetic eccentric fatigue.