## 3 Results
The LCL instead is loaded during the whole swing phase. All components of MCL and LCL (MCL-a, MCL-i, MCL-p, LCL-1, LCL-2, LCL-3, not represented in the figure) had similar behavior. The tension of the deep components of MCL and the capsular ligaments are reported in Figure 8. The MCL-dp was loaded during the stance phase, with two peaks in correspondence with maximum knee extension, while the anterior component (MCL-da) was loaded in the swing phase. Figure 8: Tension of the deep medial collateral ligament (**a**) and capsule ligaments along the stride cycle (**b**). Continuous lines refer to the “All muscles” condition; dashed lines refer to “No ground reaction forces-no muscles forces” condition. For this condition, the muscle labels are evidenced by an “**”. Figure 7: Tension of the cruciate ligaments (**up**) and collateral ligaments (**down**) along the stride cycle. Continuous lines refer to the “All muscles” condition, dashed lines refer to “No ground reaction forces–no muscles forces” condition. For this condition, the muscle labels are evidenced by an “**”. The posterior components of the capsule (Cap-Post-L and Caps-Post-M) were also recruited during the stance phase: the Cap-Post-L more continuously and the Cap-Post-M with two peaks at the early stance and late stance, respectively, and a zero tension in the middle. The tension of the anterolateral capsule (Cap-Ant-L) occupied the whole stance phase and half of the swing phase. All components of the capsule exhibited considerably reduced tension in the \"No muscles\" condition. When the simulations were carried out by sequentially removing the quadriceps or the hamstrings, the obtained results were the ones reported in Figure 9. Compared to the \"All muscles\" condition, the ACL exhibited a drastic reduction of tension when the quadriceps was removed. Only a short phase of loading remained at the beginning of the stride cycle. The removal of hamstrings instead did not affect the ACL tension, except at the end of the swing phase, where the tension appeared enhanced. Removing the quadriceps had an opposite effect on the PCL tension: The phase of recruitment during the stance phase was anticipated and lasted for the whole stance phase, with the appearance of two peaks considerably higher than in \"All muscles\" condition. The PCL recruitment in the second half of the swing phase was almost unaffected by the quadriceps removal. At contrary, the \"NoHam\" condition did not affect the PCL tension in the stance phase but drastically reduced the PCL tension in the last swing phase. Concerning the collateral ligaments (Figure 9, lower panel), the removal of quadriceps muscle produced a generalized reduction of tension in both LCL and MCL. The appearance of a short-lasting recruitment of LCL ligament at around 0.2 s is probably related to an abnormal position of the two contact surfaces that was caused by the unbalanced muscular condition. The removal of the hamstrings produced no relevant changes except at late swing phase, where the LCL tension appeared reduced and the MCL tension appeared increased. The elimination of quadriceps had a mild effect on the deep components of the MCL (see Figure 10): only in a small portion of the recruitment phase of MCL-dp the tension was appreciably reduced. The quadriceps removal had instead a considerable effect in reducing  
Figure 9: Changes of ligaments tensions obtained by removing the quadriceps group (NoQuad) or the hamstrings group (NoHam). The black curve represents the reference condition in which all muscle forces were applied in the model. the force in all the components of the capsule: Cap-Ant-L, Cap-Post-L, and Cap-Post-M. No effect was produced by the elimination of the hamstrings, except for a short-lasting increase of the tension in the Cap-Ant-L at late swing phase. The effects of the elimination of the gastrocnemius force were not included in the previous figures for the sake of clearness. Just as an example they are reported in Figure 10 with reference to the three capsular components.