## 4 Discussion
In landing scenarios, the increased knee flexion ROM is often attributed to the enhanced sense of stability provided by the knee braces. This added sense of security can reduce athletes' fear of movement and may lower the pre-activation and protective response of thequadriceps. As a result, the biceps femoris and other knee flexors become more dominant, leading to an increased knee flexion ROM [39; 40]. Alternatively, the knee brace might alter the proprioception of the knee joint by compressing the proprioceptors around the knee, thereby modifying the knee joint's proprioceptive feedback [41; 42], this, in turn, might lead the knee joint to adopt a safer landing strategy. [PERSON]'s study had shown that a greater knee flexion angle allows for a longer landing buffer time, facilitating the absorption of GRF [43]. Our study also identified significant differences in VGRF during the landing cush-ioning phase across different knee brace stiffness levels. As the stiffness of the knee brace increased, the peak VGRF decreased, which is also related to ACL injury. Some studies had shown that during the landing phase, the peak VGRF is positively correlated with the peak forward GRF, and the peak forward GRF was further positively correlated with the anterior shear force applied to the tibia [44]. Therefore, peak VGRF was considered a key indicator of ACL load. While some studies had suggested that wearing knee braces did not significantly alter the magnitude of peak VGRF during impact activities, others had reported changes in peak VGRF, possibly due to variations in the types of knee braces used. Upon ground contact, the GRF exerts pressure on the body, with the loading rate reflecting the speed at which the body absorbs these forces [45]. Compared to no stiffness, both low-stiffness and high-stiffness knee braces resulted in lower loading rates, with the high-stiffness knee brace exhibiting the smallest loading rate. External loads played a crucial role in determining the load experienced by the ACL [46]. A higher loading rate indicated that the body absorbs more GRF in a shorter period, which can impose excessive strain on the joint and increase the risk of injury, particularly during the landing cushioning phase of a pull-up jump shot. Wearing high-stiffness knee braces can effectively absorb and dissipate these impact forces, thereby reducing the risk of knee injuries. [PERSON]'s study had found that during the landing cushioning phase, the ACL experiences the highest stress [47]. This result is consistent with the trend observed in our study. This study indicated that during both phases, significant differences were observed in the knee flexion moment at peak VGRF when wearing knee braces of different stiffness levels. As shown in the results, when a no-stiffness knee brace was worn, the knee flexion moment was greater than that with low-stiffness and high-stiffness braces. This could be attributed to the GRF, which caused the quadriceps to generate a larger knee extension moment to counteract the GRF and maintain dynamic stability of the knee joint. In [PERSON]'s [7] study, subjects who wore hinged knee braces during depth jumps showed an 18% reduction in peak anterior-posterior force on the knee joint. Therefore, wearing high-stiffness knee braces helps reduce the load on the ACL. During the landing phase of the stop-and-jump shot, there was a significant correlation between the anterior shear force at the proximal tibia, peak knee flexion moment, and VGRF; female athletes exhibited a trend of synchronized increases in peak tibial anterior shear force and peak knee flexion moment [48]. The difference between low-stiffness and high-stiffness braces lies mainly in the mechanical properties. There was no obvious change in the internal and external rotation angles of the knee joint at the IC moment, which might be because the knee joint plays a horizontal fixation role when wearing protective gear of different stiffness.