The objectives of this study were to compare muscle activation time and dynamic postural variables in athletes with and without chronic ankle instability during jump-landing, followed by a choice reaction time task which was provided by the visual stimulus. Methods: Nineteen athletes [11 healthy athletes and 8 athletes with chronic ankle instability (CAI)] participated in this cross-sectional study. After informing them about the procedure and goals of the study, they started jump-landing

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... ol in response to the visual stimulus. Muscle activation time and dynamic postural control data were taken using an electromyographic (EMG) machine and force plate, respectively. Results: The results of the two-way repeated measurement analysis of variance (ANOVA) showed that there were significant differences in athletes with and without CAI for medial/lateral stability index (MLSI; tested leg effect: p=0.006); the pre-motor time of the gastroc-soleus, peroneus longus, and peroneus brevis (interaction effects of the tested leg and the tested group: p=0.001, p=0.015 and p=0.006, respectively) and the pre-motor time of the tibialis anterior (tested group effect: p=0.036). Conclusion: More attention should be on the muscle activation time because changes in this parameter may be one of the preliminary risk factors for instability, although cohort studies are required to prove it. A more challenging task with more sensitivity for differentiating between stable and unstable ankle is needed. Level of evidence: IIIb.