功能性踝關節不穩定（functional ankle instability，FAI）是指踝關節具有正常生理參數及活動度範圍，活動時卻發生「軟腳」或「難以控制」的感覺，易造成腳踝內翻扭傷傷害產生。許多研究指出可能是FAI者在著地前後的腳踝回饋穩定機轉較差，然而對於FAI者的神經反應特徵目前仍不清楚，本研究目的為探討FAI患者著地時踝部運動學與肌電圖表現情形。本研究招募12位單側FAI及12位年齡配對健康參與者，研究者以動作分析系統與肌電圖來收集其下肢在執行斜板著地測驗之著地前100毫秒與著地後200毫秒的運動學（三維關節角度）與肌電圖（腓骨長肌、脛前肌、腓腸肌與比目魚肌）資料。研究結果顯示：FAI組之患側腓腸肌活化與踝關節蹠屈角度於著地前期顯著高於健側，著地後期患側之腓骨長肌活化程度則顯著比健側弱，然而FAI組的患側與控制組兩側則皆無顯著性差異。本研究結論：FAI者的患側在開路與閉路迴路機轉皆不利於著地，但這樣的差異在FAI者與健康者之間卻仍難以區分。

Functional ankle instability (FAI) is a condition that the ankle with normal range of motion, but gets sprained easily due to poor control. Many studies found that decreased stabilizing mechanism existed in open and closed loop feedback during pre- and post-landing. However, little is known about the detailed neuromuscular functions in subjects with FAI. The purpose of this study was to determine the patterns of kinematics and electromyography of ankle during a tilted landing task. Twelve subjects with unilateral FAI and 12 age-matched healthy controls were recruited in this study. Researchers measured the 3D ankle kinematics (average and peak joint angle) and electromyography (the peroneus longus, tibialis anterior, gastrocnemius, and soleus muscle) during the titled ground landing task for the periods of 100 ms pre- and 200 ms post-initial contact (IC). The results were as follows: Patients with FAI had significantly higher gastrocnemius activity and the plantar flexion in the affected side compared to the sound side during pre-landing. The peroneus longus activity in the affected side was significantly lower than the sound side during post-landing. However, no differences were found among affected side of FAI patients and both sides of control. These findings conclude that open-loop and closed-loop neuromuscular controls in patients with FAI may be disadvantageous during tilted landing task, but they could develop a compensation action to imitate the tilted landing of the healthy controls.