## 5 Conclusions  
A methodology based on finite element (FE) analysis (FEA) and experimental techniques for designing the elastic elements of prosthetic feet and their functionality verification is presented. The present methodology can be exploited for different purposes. It can be used to design new configurations of energy-storing and -releasing (ESR) feet for different weight categories. It can be applied as a tool to study new systems that can be added to an existing ESR foot to change its stiffness/damping properties. Furthermore, it can be used to study the behavior of active prosthetic feet where their working principle relies on actuators combined with the elastic foot. The methodology is subdivided into \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Step** & **Type of Simulation** & **Number of Nodes** & **Number of Deg. of Freedom** \\ \hline
1 & 2D Static & 10,000 & 20,000 \\
2 & 3D Static & 600,000 & 1,800,000 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Number of nodes and number of degrees of freedom from the 2D FE model (Section 3.1.1) and the 3D FE model (Section 3.1.2). Figure 30: The lower leg prosthesis behavior when subjected to the ISO 22675 roll-over test. Figure 31: The rotation of the foot prosthesis when subjected to the ISO 22675 roll-over test. three main phases: the _design phase_, the _validation phase_ and the _functionality verification phase_. The _design phase_ consists of two steps based on FEA. In the _validation phase_, the FE models are validated through a static test on physical prototypes. In the _functionality verification phase_, two standard dynamic tests from ISO 10328 and ISO 22675 are simulated. In the case study of the ESR foot MyFlex-\(\gamma\), the static 2D FE model from the first step of the _design phase_ resulted to be a reliable and fast-response tool to predict the influence of geometric parameters on the behavior of the ESR foot. In addition, the 2D FE model resulted to be a reliable instrument to find the optimal values of these geometric parameters. With the static 3D FE model (the second step of the _design phase_), it was possible to optimize the material properties of the composite elastic elements. By optimizing the geometry and the material properties, it was possible to obtain the correct stiffness of the foot prosthesis for a specific weight category of users, providing a device with a safety factor of 4. The stiffness curves obtained from the 3D model resulted comparable to the results from the ISO 10328 equivalent mechanical test (_validation phase_). Therefore, the FE models can be considered validated. The rotation angles of the foot obtained in the model based on the dynamic test ISO 10328 and the model based on the dynamic test ISO 22675 are within the target range of motion. The two dynamic tests can be considered alternatives to each other. They can be both considered helpful for a preliminary assessment of the prosthesis dynamic behavior before testing the prototype with amputee users. Conceptualization, J.T., T.M.B. and M.O. ; methodology, J.T., T.M.B, M.P., M.L. and M.O. ; validation, J.T., T.M.B. and M.L. ; formal analysis, J.T. ; investigation, J.T., T.M.B. and M.L. ; data curation, J.T. ; writing--original draft preparation, J.T. ; writing--review and editing, J.T., T.M.B, M.P., M.L., M.O., R.C. and A.Z. ; visualization, J.T. and A.Z. ; supervision, M.O., R.C. and A.Z. ; resources: M.O., A.Z. and M.P. ; project administration, M.O., R.C. and A.Z. ; funding acquisition, R.C. and A.Z. All authors have read and agreed to the published version of the manuscript. This work was funded by the European Commission's Horizon 2020 Programme as part of the project MyLeg under grant no. 780871. The authors want to thank [PERSON] and [PERSON] (MSc students at University of Bologna) for their fundamental contributions to the design and manufacturing of MyFlex-\(\gamma\).