## 4 Discussion
There seems to be little awareness of the EDL's fundamental role in achieving balanced dorsiflexion during the pre-positioning of the foot on the ground and providing foot clearance during the swing phase of gait. With the support of the simulation results presented in this study, we would like to emphasise the importance of measuring EDL activity during the gait of EVFD patients. Most of these patients typically present several combinations of overactivity and shortening of the plantarflexor muscles. This antagonises the mechanical effect of the dorsiflexors, inevitably leading to the equinus deviation [26]. In our study, we mimicked this outcome by gradually shortening the SO. Our simulations show that even a mild reduction in SO extensibility is sufficient to prevent adequate foot dorsiflexion, which cannot reach the neutral position (Figure 5A). Most likely, this could result in an increased risk of stumbling during walking and may induce the subject to compensate for such limitations by adopting strategies involving other lower limb districts [14; 43; 44; 45]. Therefore, from a clinical perspective, maintaining the length and extensibility of the triceps sureae must be a priority for rehabilitators to be considered already in the acute phase after a stroke [46]. Looking at Figure 5A, it may be surprising to see plantarflexion occurring during TA contraction as soon as the limit of the SO length is achieved. To explain this paradox, it must be noted that TA shortening causes forefoot supination and calcaneus inversion (Figure 5B,E). The force needed to shorten the TA increases abruptly (Figure 5F). The calcaneus inversion occurs about the talocalcaneal axis, while the forefoot supination results from a combination of movements about the talonavicular joint and the cuboid-calcaneal joint. The association of these two movements produces the supination and adduction of the forefoot. With the foot supinated and adducted, the part of the foot intersecting the plane where the dorsi-plantarflexion angle is measured is the lateral side. Since during supination the first metatarsus moves upwards and the fifth metatarsus moves downwards, the angle measured in that plane corresponds to plantar flexion. Figure 7 can help us better understand this phenomenon. This situation is common with neurologic patients (e.g., after a stroke). The upward movement of the first metatarsal head following foot supination should not be interpreted as mild dorsiflexion since the foot crawls on the floor in this case. When considering the combined contraction of the TA and EDL, the forefoot supination is prevented by the balanced activity of these two muscles. When SO extensibility is limited, their action results in calcaneus inversion. This can be seen in Figure 6E). Of course, this mechanical solution entails a considerable increase in the TA and EDL force (panels F, H) and is necessarily limited to a small degree of foot dorsiflexion (panel A). It is worth mentioning that we simulated the effect of plantar flexcor contracture by exclusively limiting the length excursion of the SO. This may appear oversimplistic since the resistance to foot dorsiflexion can be caused by several other factors: increased muscle stiffness, increased muscle viscosity and muscle overactivity [37,38]. However, they all result in a hindrance to the normal length excursion. Our data tested different degrees of length limitation, and it can provide insight into the effects of such a phenomenon.