## 4 Discussion  
The main goal of this study was to investigate the effect of long-duration running training, which simulates the running load of a typical basketball match, on ACL strain during CM movements, which can indicate the risk of injury to ligaments. The second objective of this study was to investigate the changes in CM before and after the running training load to possibly identify specific lower extremity biomechanical characteristics that may be linked to high-risk ACL injuries. To explore changes in ACL strain we used a  
Figure 7: The results of PCA. PCA score plots demonstrate the biomechanical characteristics of 90\({}^{\circ}\) CM in pre-IR training. (**A–C**) demonstrates knee moments score based on the high and low levels of ACL strain during 90\({}^{\circ}\) CM; (**D–F**) demonstrates knee angles score based on the high and low levels of ACL strain during 90\({}^{\circ}\) CM; (**G–I**) demonstrates knee force score based on the high and low levels of ACL strain during 90\({}^{\circ}\) CM. The confidence interval of 95% was utilized as the clustering criterion for all PCA score plots. model approach using OpenSim where ACL was presented as a nonlinear elastic passive soft tissue. To check the reliability of the model we also collected the electrical activity of the lower limb muscles to compare with CMC results. According to [PERSON] et al. [56], who demonstrated that human knee ligaments strain was typically up to 5% of the original ligament length during dynamic tasks. In contrast we observed twice as great elongation in the ACL at each condition. This can be explained by the different task and method to calculate ACL strain which was used in these studies. Furthermore, it has been suggested that micro-fiber damage and ACL rupture can occur when the strain reaches a percentage value between 9 and 15% [45]. ACL elongation in this study was simulated in OpenSim, which primarily calculates the length changes according to the kinematics of the knee combining with the ground reaction force data. The difference of CM characteristics in this study before and after the running training load is hard to compare with other studies because most reports used different protocol to induce fatigue, thus the outcome regarding the lower limb biomechanics is conflicting [57; 58]. It has been suggested that incorporating targeted strength training could be a crucial factor in preventing ACL injuries [59]. We observed that ACL strain is lower (i.e., less elongation) after completing 5 km of IR training during each CM condition. It can be assumed that the highest strain was observed during the CM 90\({}^{\circ}\), while the lowest strain was observed during CM 180\({}^{\circ}\). Mechanical strain refers to the magnitude of elongation of a tissue relative to its resting length. Since ligaments cannot change their length by themselves, elongation of ligaments is induced by joint movement, and the amount of ligament lengthening depends on the amount of joint displacement and the magnitude of forces that stretch the ligaments. Therefore, the highest strain was observed during the initial ground contact when the ACL was elongated the most and during the takeoff phase where the knee extensor muscle generates high forces to accelerate the body. The alterations in ACL strain following the running training load demonstrated a decrease in each CM condition, implying that fatigue may trigger an elevation in ligament rigidity that leads to diminished elongation. Conversely, the CM condition showed higher knee flexion following the training, which may have resulted in greater ACL elongation due to the observed increase in knee joint force during peak knee joint flexion. Thus, the lower strain can only be attributed to the changes in ligament stiffness induced by fatigue. Although the ACL strain was lower in CM 135\({}^{\circ}\) and CM 180\({}^{\circ}\), the difference was not statistically significant during most of the stance.