# Analysis of Different Stop-Jumping Strategies on the Biomechanical Changes in the Lower Limbs
## 1 Introduction  
Termination tasks are common movements in basketball, volleyball, and soccer [1, 2]. These movements include stop-jumping, landing and side-cutting, etc. According to a previous study, these types of termination tasks could cause significant injuries to athletes and have a significant effect on competition performance. This is related to the fact that athletes place large loadings on their knee joints repeatedly during the performance of these tasks [3]. Many researchers have attempted to seek as much information as possible about the in vivo mechanism or cause of injuries before they occur. An example of this is the parameters of biomechanical of the lower limbs as an essential index for injury prevention [4]. The stop-jumping task is one of the most important technical actions used in basketball, and it can be divided into three steps. [PERSON] and [PERSON] define what a complete stop-jumping task is [5, 6], whereby the participant performs an approach run, then immediately stops (horizontal landing phase), and finally takes off. Anterior cruciate ligament (ACL) injuries were studied for many years [7, 8, 9, 10, 11], and many researchers attempted to help athletes decrease ACL injuries when performing a sharp deceleration task [12, 13]. These include stop-jumping, a quick stop, or a cutting maneuver. A previous review observed that there was 70% chance of non-contact ACLinjuries in stop-jumping tasks [14]. Therefore, we need to understand what the key information required is for understanding the biomechanical parameters before ACL injuries occur. The knee flexion angle is one of the most important indexes to reflect ACL injuries. According to previous studies, a higher ground reaction force (GRF) on the vertical landing could impact the lower angle of knee flexion at the horizontal landing phase during the stop-jumping task. As a result, decreasing the angle of knee flexion could raise the loading on the ACL [15, 16, 17, 18, 19]. The angle of knee flexion needs to be considered as a significant biomechanical parameter for evaluating ACL injuries. Further reasons for detecting the cause of ACL injury are that many patients following reconstruction of ACL surgery commonly suffer potential risks for further injury. Previous studies followed patients who accepted the reconstruction of ACL surgery [20, 21], and they found that there was a 30-35% chance for the patient to suffer a second ACL injury. The body is supported by the legs separately, and if one side undergoes cruciate ligament reconstruction, the load of the lower extremity on the other side is inevitably increased. This is one of the most important highlighted risks for patients who suffered second ACL injuries [22, 23, 24, 25, 26, 27]. [PERSON] further demonstrated that the knee extension moment was a further biomechanical parameter for consideration when reconstructed ACL surgery patients performed landing mechanics [25]. A previous study focused on patient follow up after reconstruction of the ACL, and they noted that 87% patients had the potential of osteoarthritis following the results of an imaging test, with 45% needing re-surgery and with only 23% of patients being content with their function of the knee [28]. Posterior ground reaction force (PGRF) and proximal tibia anterior shear force (PTASF) are more likely to reflect or present the signs of ACL injuries. Previous studies revealed that this can be the most direct loading mechanism for ACL injuries [29]. This research analyzed PTASF by using a simulation of biomechanical parameter indexes, and the researchers proved that PTASF raises the drawer force of the anterior of the knee, which has a positive correlation with ACL injuries. As for the index of PGRF, the study previously indicated that many different movements contributed to non-contact ACL injuries, because they have the same characteristics mimicking a sharp deceleration of the body [1, 30, 31].