Study On The Reaction Time Of Action In The Ankle Joint With Functional Instability

Objective: Ankle sprain is a common phenomenon in sport. Functional ankleinstability (FAI) can lead to ankle sprain recurrently. The reason of functional ankleinstability was unknown. In order to explore the reaction time of the ankle joint and theeffects of the different fatigue modes, and to provide experimental reference fordiagnosis, prevention and rehabilitation evaluation of functional ankle instability, thereaction time of action was investigated in the ankle joint of functional instability withplantar flexion and dorsal flexion,Methods： The ankles of30college-aged males were tested in this study. Fifteenof the subjects had unilateral FAI, while the other15subjects were matched-paired andserved as controls. The CON-TREX isokinetic dynamometer, light signal generator andthe biovision system were synchronously used to collect signal of light, torque andelectromyography. The tester gave a cue to the subject and triggered the power of thelight signal generator. The Subject controlled the ankle joint plantar flexion ordorsiflexion as soon as possible once he saw the light signal changed. Then he mustkeep the act for5seconds. The original data were recorded at the same time. Theoriginal signal was processed through Matlab7.0and Dasylab8.0. The total reactiontime (TRT), pre-motor time (PMT) and electro-mechanical delay (EMD) werecalculated. There were four modes leading to the muscular fatigue. They are isokineticconcentric/concentric contraction, isokinetic eccentric/eccentric contraction, isokineticpassive/concentric contraction and isokinetic concentric/passive contractionrespectively with the velocity of60°/s. There was an interval of one week between thesuccessive tests modes and the either ankle of each subject was tested in a random order.A multivariate repeated measures ANOVA was used to determine time-dependentdifferences and the differences between before and after fatigue in reaction time between the two groups with FI and without FI, among the different fatigue modes. Thet test was used to determine the differences between the two groups with FI and withoutFI before fatigue. The ANOVA was used to determine the differences among thedifferent fatigue modes.Results:(1) There was no significant difference between FAI and control groupsbefore fatigue. However, after the eccentric/eccentric fatigue, the TA EMD、GM EMDand PL EMD of FAI group were significantly longer than those of control group（P＜0.05）. After the concentric/passive fatigue, the TA EMD with FI were significantlylonger than that of control group（P＜0.05）. After the passive/concentric fatigue, theSO EMD and GM EMD with FI were significantly longer than those of control group（P＜0.05＝(2) The EMD of ankle after fatigue was longer than that before fatigue ineach group. The TRT of both groups before fatigue was longer than that after fatigue（P＜0.05＝After the dorsal flexion fatigue. There was no significant difference before andafter fatigue in TA PMT. The SO PMT、GM PMT and PL PMT of ankle of FAI groupwere shorter than those of control group, while there was no significant difference in theTRT of plantar flexion between before and after fatigue.(3) There were significantdifference among the different fatigue modes in the SO PMT、GM PMT、GM EMD andPL PMT of FAI group after fatigue. The SO PMT、GM PMT and PL PMT, after theisokinetic concentric/concentric fatigue, were longer than those after isokineticconcentric/passive fatigue. The SO PMT、 GM PMT after isokineticconcentric/concentric fatigue were longer than those after isokinetic concentric/passivefatigue. The SO PMT、GM PMT after isokinetic concentric/concentric fatigue werelonger than those after isokinetic passive/concentric fatigue（P＜0.05）.The GM EMDafter isokinetic concentric/concentric fatigue was shorter than that after isokineticpassive/concentric fatigue（P＜0.05）. The GM PMT after Isokinetic concentric/concentric fatigue were longer than that after eccentric/eccentric fatigue（P＜0.05）. TheGM EMD after Isokinetic concentric/passive fatigue were shorter than that afterisokinetic passive/concentric fatigue（P＜0.05）. There were no significant differencesin the other dependent variables of reaction time among the four modes of fatigue.Conclusion：(1) Before the ankle muscular fatigue，there were no significant differences in the reaction time of action between functional unstable ankle and normalankle.(2) The EMD of ankle muscle was prolonged after local muscle fatigue, while theTRT of dorsiflexion action was longer and the PMT of triceps surae was shorter.(3)After the local muscle fatigue, EMG mechanical delays, of functional instability ankle,were longer than that of normal ankle; the muscle of functional instability ankle wasinclined to get tired easily，which could provide experiment evidence for the diagnosisof the functional ankle instability.(4) After the local muscle fatigue, for the PMT of theplantar flexion muscle and EMD, there were significant differences among the differentfatigue modes. It can guide the athletes, who with functional ankle instability to selectappropriate exercise load and muscle contraction type scientifically during the exercisetraining and rehabilitation training.