Abstract Introduction: High synergy at gait initiation and the similarity of this movement pattern to the mechanisms that cause ankle sprain injury and subsequent chronic ankle instability are among the reasons that require research into control changes in gait initiation. Therefore, aim of the present study was to investigate the changes in the dynamic posture stability index of gait initiation in professional footballers with chronic ankle instability injury. Methodology: The present study was applied type and causal-comparative research that examined the gait initiation in professional footballers with chronic ankle instability injury (CAI) by considering changes in dynamic posture stability index. The mean age (years) of the subjects in the CAI and control groups were 22.3± 0.7 and 23.2± 9.3, respectively. For this purpose, from two KISTLER 9286A Force plate with a frequency of 100 Hz were used. After extracting the research variables, mean and standard deviation values were used to describe the data, shapiro-wilk test for normality and independent t-test at a significance level of 0.05 was used to compare the values between groups. Results: Dynamic posture stability index in the directions; Anterior-posterior (APSI), Medial-lateral (MLSI), Vertical (VSI) and Overall (DPSI) in CAI and control groups were examined. Dynamic posture stability index of gait initiation, which reflect the kinematic activity of the center of pressure and the center of mass, showed better performance in all directions in the CAI group due to the lower number of records (less sway was observed in center of pressure). However, no significant difference was observed between the two groups (p> 0.05). Conclusion: It seems that the superiority of the CAI group in dynamic posture stability index parameters compared to the control group can be related to the nature of the activity performed (gait initiation), which is a combination of static and dynamic activity. So, to rehabilitation specialis
