Background: Balance impairment is a common consequence of chronic ankle instability (CAI). This study aimed to assess the discriminative validity of four clinical tests for quantifying balance impairment in individuals with CAI. Methods: Participants were screened for their balance using the single-leg balance test (SLBT) and were assigned to either the positive or the negative SLBT groups. Fifty-four individuals with CAI (N = 27 per group) were recruited and completed four clinical tests including the foot-lift test (FLT), the time-in-balance test (TIBT), the modified star excursion balance test in the posteromedial (mSEBT-PM) direction and the side-hop test (SHT). The receiver operating characteristics (ROC) curve coupled with Youden index were calculated to determine the optimal cut-off scores of each test. Results: We found significant differences in balance between groups for all tests, with good to excellent values for the area under the ROC curve (AUC). All four tests reached good to excellent sensitivity and specificity values and had significant cut-off scores to discriminate balance performance among CAI participants. Conclusion: All four clinical tests can be conducted with their respective cut-off scores to quantify balance impairment in individuals with CAI.

Background: Individuals with chronic ankle instability (CAI) have poor postural stability, functional limitations and low quality of life. Although nine-square exercise can improve postural control, there is limited evidence demonstrating whether it can function as an alternative CAI rehabilitation programme. This study aimed to determine the effects of nine-square exercise on postural stability and self-reported outcomes in individuals with CAI. Methods: Eighteen male collegiate athletes with CAI participated in either a 6-week nine-square exercise or a control group (n = 9 per group). At baseline and post-intervention, the participants undertook clinical tests to measures dynamic and static postural control, and self- reported outcomes regarding ankle stability and function. Results: Within-group differences, the nine-square exercise group experienced improved dynamic postural control (P = 0.004), static postural control (P = 0.001) and self-reported outcomes (P < 0.05). For the control group, only static postural control improved (P = 0.018). Post- intervention, the nine-square exercise group experienced significant improvements in dynamic postural control (P < 0.001), ankle stability (P = 0.002) and functional ability (P < 0.05) relative to the control group. Conclusion: These findings suggest that the nine-square exercise can offer an alternative rehabilitation programme for improving postural control, self-perceived ankle stability and functional ability in CAI.

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