The Neuromuscular Control of the Ankle Joint in Subjects with Functional Ankle Instability

Background and purpose: Functional ankle instability (FAI) is considered a major cause of recurrent ankle sprains in athletes. Researchers have proposed that altered neuromuscular control in the lower extremities as the major contributor to FAI. However, inconsistent findings were reported regarding muscle activation and reaction time in FAI sufferers, probably due to variations in the testing parameters among studies. The purposes of this study was to investigate the effects of testing parameters on the measurement of muscle reaction time and muscle activation of the peroneus longus, tibialis anterior, and soleus during sudden inversion and single leg landing tests, and to compare the differences in these measurements between subjects with and without functional ankle instability (FAI). Methods: Fourteen subjects with FAI and 14 matched controls were recruited for this study. Three inclination angles: 15°, 30°, and 45° and three landing heights: 25, 35, and 45 cm were used for the sudden inversion test and single leg landing test respectively. Muscle activities and reaction time of tibialis anterior, peroneus longus and soleus in control and FAI groups were recorded bilaterally using a surface electromyography system (Telemyo 900, Noraxon USA Inc., AZ, USA). Statistical Analysis: Two-way repeated measures analyses of variance (ANOVA) was used for statistical analysis. The level of significance was set at α=0.05. Results: Testing inclination angle and landing height had a significant impact on the measured muscle activities (p＜0.005) and muscle reaction time (p＜0.001). Compared to the control group, significantly shorter peroneal reaction time (p=0.03) and decreased peroneal (p=0.03) and soleus (p=0.04) muscle activation were identified on the involved side in subjects with FAI. Conclusion and Clinical Relevance: The testing parameters influenced the results of the muscle performance measurement. The reaction time and activation amplitude of the peroneus longus and soleus muscles were altered in subjects with FAI. Further studies should take into consideration the effect of testing parameters, and investigate the mechanisms behind the changes of the muscle performance in subjects with FAI.