Abstract
Repeated ankle sprains would result in functional instability (FI), and decrease the proprioception sensitivity and the postural control ability. It also demonstrated that ankle sprain might impair the nerve conduction or neuron pathway surrounding the ankle joint. However, no study has investigated the influences of FI on motoneuron excitability. The purpose of this study compared the difference in proprioception and the Hoffmann reflexes between FI and normal health (NH) ankles. Twenty-one subjects (9 healthy, 3 unilateral FI, and 9 bilateral FI) were recruited. The proprioception was measured by the Biodex Ⅲ dynamometer as ankle active/passive reposition sense. The soleus Hoffmann reflex was measured by Dantec Keypoint as H-reflex and M wave maximal amplitude. An independent ttest and a Pearson correlation analysis were used to examine the difference and relationship between FI and NH ankles. The statistic significance was set at p<.05. The results of this study showed that FI ankle had a greater absolute reposition error angle but smaller H-reflex maximal amplitudes than the general population. This study demonstrated that the FI ankle had a significantly poor proprioception and a lower motoneuron excitability. It is suggested that the decreased sensitivity of ankle proprioception might be due to the impaired mechanoreceptors in the functional instability ankle. In addition, the lowered maximal amplitude of the Hoffmann reflex might be due to the diminished numbers of the neurotransmitter released by the afferent terminal.