Ground reaction force data in functional ankle instability during two cutting movements.
BACKGROUND: Functional instability of the ankle joint may interfere with proper execution of quick cutting movements in sports. Previous studies have provided information regarding the ground reaction force characteristics in such movements in healthy players but no research was found in players with ankle instability. The purpose of this study was to evaluate and compare ground reaction forces in functionally unstable ankles with healthy ones during two cutting movements, the v-cut and the defensive shuffle. METHODS: Fifteen male basketball players with self reported unilateral functional instability and 17 matched controls, performed three v-cuts and three defensive shuffles on two synchronised force platforms. Both joints were tested and ground reaction forces analysed by an one-way ANOVA for independent groups to test differences between groups, and paired t-test to examine differences within affected players. FINDINGS: Unstable ankles, demonstrated significantly greater first vertical force peak, than contralateral unaffected joints (P < or = 0.05) and lower relative time to peak than controls (P< or = 0.05), during v-cut movement. No significant differences were seen in variables between groups during lateral shuffling. INTERPRETATION: Unstable ankles demonstrated altered patterns of ground reaction forces, with a rapid onset of high vertical force during the first millisecond post-impact, while the medial component was unchanged. Although the increased vertical forces are considered predisposing factors to repeated injury, this finding is likely a neuromuscular response making the ankle joint more stable avoiding excessive inversion forces.