## 3 Results
### Effect of TA, EDL and TA + EDL Contraction on Dorsiflexion  
Figure 3 shows the positioning of the foot model obtained when the foot was hanging freely and prior to placing muscle forces and at the end of TA, EDL and TA + EDL simulated contractions.  
The activation of TA alone produced very mild dorsiflexion, while forefoot supination was the most relevant movement. On the contrary, the activation of the EDL determined forefoot pronation but still negligible dorsiflexion. Only the simultaneous and balanced activation of both TA and EDL produced dorsiflexion and negligible pronation/supination. The analysis of the foot joint angles confirms this qualitative observation (see Figure 4). The range of motion obtained for each of the angles considered is summarised in Table 1.  
When TA and EDL contracted separately, the muscle forces at the end of the movement were 152 N for the TA and 50 N for the EDL. When both muscles were contracted simultaneously, the force was 210 N and 25 N, respectively.  
Figure 5 presents the effects of limiting the length excursion of the SO during the contraction of TA. The following effects could be observed:  
* Foot dorsiflexion produced by the TA was progressively limited as far as the SO was constrained to shorter excursions. After that limit, the effect of the TA contractions switched from dorsiflexion to plantar flexion (panel A);
* Forefoot supination increased more rapidly as soon as the SO length achieved its limit (panel B);
* Talus dorsiflexion about the tibia was stopped while the first metatarsus increased in dorsiflexion (panels C and D);
* The calcaneus inversion increased more rapidly (panel E);
* The force of the TA increased considerably as long as the SO lengthening was reduced.  
Figure 6 presents the effects of limiting the length excursion of SO during the simultaneous contraction of the TA and EDL. These effects can be described as follows:  
* Foot dorsiflexion slows down and comes to a stop as the limitation of the SO lengthening progresses (panel A);
* Forefoot pronation and the latiobtial dorsiflexion stop at different angles in correspondence with the SO lengthening limitation (panels B and C);
* Dorsiflexion of the first metatarsus is affected differently at the beginning of the movement (SO lengthening limited at 25%) than at the end (SO lengthening capped at 75%). In the former case, dorsiflexion increased; in the latter, dorsiflexion lessened (panel D);
* The calcaneus undergoes a sharp inversion as soon as the SO lengthening stops (panel E);
* The contraction force of both the TA and EDL abruptly increases when SO lengthening is halted (panels F and H).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Joint Rotation** & **Initial** & **TA** & **EDL** & **TA + EDL** \\ \hline Forefoot dorsiflexion & \(-18^{\circ}\) & \(18^{\circ}\) & \(12^{\circ}\) & \(39^{\circ}\) \\ Forefoot supination & \(12^{\circ}\) & \(18^{\circ}\) & \(-25\) & \(16^{\circ}\) \\ Talotibial dorsiflexion & \(-13.5\) & \(18.5^{\circ}\) & \(6^{\circ}\) & \(30.5^{\circ}\) \\ First metatarsus-talus dorsiflexion & \(-4^{\circ}\) & \(4^{\circ}\) & \(3^{\circ}\) & \(5.6^{\circ}\) \\ Calcaneus inversion & \(1.2^{\circ}\) & \(4.8^{\circ}\) & \(-5.6^{\circ}\) & \(-3^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Amplitude of the movement obtained by the simulated contraction of the TA, EDL and TA + EDL. The first column reports the angles at the beginning of the simulation when the foot was suspended off the ground.  
Figure 5: The effects of limiting the length excursion of the SO during the contraction of the TA. Different colours represent the effect of different allowed length excursions: from 100% (black curve), indicating no limitation, to 25% (yellow curve), indicating that the SO can only lengthen by 25% of its full range. Foot joint angles are reported in panels (**A**–**E**), dorsiflexors muscle force in (**F**), SO muscle length in (**G**).