Introduction: 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 protocol 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 mea-surement 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 mus-cle 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.