## 4 Discussion  
We showed that, during deceleration, participants landing in the knee valgus position experienced greater negative mechanical work at the knee joint, compared with those landing in the knee varus position. Similarly, they had greater knee extensor moments at the instant of the maximum knee flexion, and greater knee extensor angular impulses. This explains the net joint moments experienced by the lower extremity joints during DP of landing. When landing in the knee valgus position, participants experienced less negative mechanical work at the hip, compared with those landing in the knee varus position. They also had lower hip extensor angular impulses during DP. Negative mechanical work represents energy absorption through eccentric muscular contraction [38]. [PERSON] et al. reported that biomechanical factors, related to ACL injury are influenced by the magnitude and timing of energy absorption at the lower extremity joints during landing [39]. Therefore, changes in the lower extremity energy absorption capacity, brought on by altering knee alignment during landing, are likely to be effective in eliminating biomechanical components of the ACL injury mechanism. This study demonstrated that landings in the knee valgus position induced a characteristic energy absorption strategy with less energy absorption at the hip, and greater energy absorption at the knee during DP of landing. Thus, knee valgus alignment may increase the load on the knee joint and decrease the load on the hip joint during landing. Because a higher load applied to the knee joint can cause knee injuries during sporting activities [8; 9], greater energy absorption capacity at the knee should be avoided by adopting knee varus alignment during landing. Previous reports have indicated that the knee joint is the most important impact absorber within the lower extremities during landing [5; 6; 7]. [PERSON] et al. reported that the hip extensor, knee extensor, and ankle plantar flexor muscles in females contributed 18%, 47%, and 35%, respectively, to total energy absorption during natural landing [5]. By contrast, the present study showed contribution ratios to total negative mechanical work in the hip, knee, and ankle joints of \(5.8\pm 5.6\%\), \(46.8\pm 6.8\%\), and \(47.5\pm 7.4\%\), respectively, in the valgus group, and \(17.2\pm 6.3\%\), \(36.1\pm 9.0\%\), and \(46.7\pm 11.7\%\), respectively, in the varus group. Thus, the energy contributions in the valgus group were smaller in our study than those reported in the previous study, while the energy contributions in the varus group were larger. Nonetheless, the results indicate that landing with knee valgus may lead to poor energy absorption contribution by the hip joint. The results also demonstrate that the knee joint in the valgus group was the most important contributor of the energy absorption of the lower extremity joints. By comparison, the varus group showed a smaller contribution toward energy absorption by the knee joint and an increased contribution for energy absorption by the hip joints. These findings supported the notion that part of the knee joint's role as energy absorber could be translated to the hip joint in the participants who land in the knee varus position. The present study was carried out using the drop vertical jump test, which included both a drop landing and a second jump, as an experimental method, whereas a drop landing completed without a  
Figure 4: The negative mechanical work in lower extremity joints and knee valgus and varus angles. The mutual relations between negative mechanical work done at the hip (**a**), knee (**b**), and ankle (**c**) and the knee valgus/varus angles of each participant. second jump after landing was used in a study by [PERSON] and [PERSON] [1]. Despite the different landing methods, the two studies agree that both stiff landing [1] and landing in the valgus position tend to lead to increased energy absorption contributions by the knee joint.