## 4 Discussions and Recommendations
There are many differences between the methods utilized in papers regarding the application of material properties if different options are being explored. Starting with the skin section of the body, the use of a linear isotropic elastic material property with an  
Figure 5: Pie Charts showing the percentage of methods used to acquire data for model generation (**left**), type of geometry created (**middle**), and skin modeling methodology (**right**). elasticity of 0.15 MPa is appropriate when the skin is not combined with the soft tissues. The next layer is the soft tissues, which includes the muscles, ligaments, and fat. As portrayed in Figure 6, the use of a hyperelastic material property to model the soft tissues is the most used method; however, the choice of which hyperelastic model to use varies depending on the model created in the previous step. When the skin is combined with soft tissues, then [PERSON] et al. 's [45] Mooney-Rivlin hyperelastic material modeling is suitable. If the skin is modeled separately, then [PERSON] et al. 's [44] Mooney-Rivlin hyperelastic material modeling should be utilized. The neo-Hookean model used by [PERSON] and [PERSON] et al. [47] does not provide accurate prediction at large strains, which is ideal when the results that are being looked at are focused on the pressure distribution rather than the stress values at specific locations [19]. Finally, the Ogden model is best for use in the analysis of the rubber-like components of soft tissues. The bone layer is modeled as a rigid material with a Young's modulus between 10,000 and 12,000 MPa, a density of 1100 to 1700 kg/m\({}^{3}\), and a Poisson's ratio of 0.3. In the case of pressure ulcer studies, the parts that affect the generation of pressure ulcers are modeled using a Young's modulus of 180,000 MPa, a density of 6000 kg/m\({}^{3}\), and a Poisson's ratio of 0.3. Similar to soft tissue material modeling, hyperelastic models can be used in seat material modeling. However, the type of foam used in the design dictates which model is appropriate regarding implementation. When meshing the geometry, four-node tetrahedron elements yield the most accurate results when compared to other meshes. Consequentially, the papers that selected a four-node tetrahedron element and applied it to geometrical models contributed the most to the solution, such as soft tissues and seat foam sections, as they are in direct contact with each other and cause contact stress that affects the pressure distribution results needed as a measure of comfort. In the pressure ulcer research cases, a more complex type should be used, such as 8-node and 10-node hexahedron elements. In conclusion, the selection of mesh element types is based on the trade-off between the efficiency and accuracy of the results because the more detailed the element is, the more time consuming the simulation; this decision is usually made based on the available resources. The final step before processing the results is the application of boundary conditions. The gravity approach is the most common approach used by researchers, as it provides the advantage of being realistic when seating simulations are being conducted. However, in the case of pressure ulcer studies, the gravity approach is applied differently. Here, to obtain more accurate results, the body weight is divided among the body parts. Future Research DirectionsThis review paper covers the methodologies used to perform FEA simulations for seat comfort and pressure ulcer determination. These simulations provide insight into the external forces acting on the human body while also providing the designer of seats/beds with the capability to include multiple computer-simulated design configurations in their design methodology and to compare the results of different design configurations to find  
Figure 6: Skin material modeling options and the percentage of the method most used in the research papers included in this review [44; 45; 47; 48].