Introduction: Numerous studies have investigated the impact of kinematic and kinetic factors on the high incidence of anterior cruciate ligament (ACL) injuries among athletes. However, limited attention has been given to stride length alterations during running, specifically in athletes who have undergone ACL surgery. This study aims to examine stride length changes in the running cycle of athletes with and without a history of ACL surgery, utilizing an instrumented treadmill.

Research Methodology: 30 athletes (15 healthy athletes and 15 athletes with a history of anterior cruciate ligament surgery in the last 8-5 months ) participated in the study in the sports of football(14 people), futsal(8 people), karate(2 people), taekwondo(2 people), volleyball(4 people).Initially, the zebris Medical GmbH Germany treadmill was calibrated with a recording surface of 1.70 ×0.65 meters and a sensor area of 1.36 ×0.64 meters, which includes 10240 sensors measuring 0.85 ×0.85 CM and a range of 1-120 Newtons per square centimeter, and during this time the person was not standing on the treadmill;then the person was on the treadmill it's set, and for more preparation with 5 minutes of warm-up, They started on the treadmill and then started running at the desired speed(9 kilometers per hour for 2 minutes). .To further match the person and find their natural running state, we first allowed the short time to run at the desired speed without recording the data, and then we started recording the data.
Using information extracted from the treadmill, step length changes in both groups were investigated.The data analysis was carried out by SPSS version 26. Independent t tests were used to investigate possible differences between the group at the 95% significance level (p≤0.05).

result: Results showed that the mean and SD values in the healthy group were 162.4176±16.22 and in the ACLR group were 161.62± 14.01, and the statistical value of T was 0.14 and the statistical value of p was 0.89 (p>0.05). Therefore, there was no significant difference in stride length in the running cycle between athletes with and without a history of ACL injury in 5-8 months after surgery.
conclusion: Based on our findings, changes in stride length do not serve as a reliable predictor for preventing ACL re-injury. However, due to study limitations (such as dissimilarities in athletes’ sports fields and variations in grafts used during surgery), we recommend employing the kernel density estimation method for further analysis to analyze the curves’ behavior in both groups.