## 4 Discussion  
This study offers valuable insights into the performance of EAFs under head impact, providing new avenues for reducing the risk of fall-related head injuries in high-fall-risk environments. While previous literature has discussed that compliant materials indeed decrease the risk of head injury, this study highlights that more can be done in terms of risk prevention with the different energy-absorbing mechanisms and capabilities. The FE models of four commercially available EAF products were established based on mechanical  
Figure 8: Comparison of peak von Mises stresses (MPa) of four energy-absorbing floors in the accident reconstruction case: the former is at 2 ms and the latter is at the maximum deformation state, respectively. (**a**) Igelkott Floor; (**b**) Kradal; (**c**) SmartCells; (**d**) OmniSports. Figure 9: Energy in head impact simulation (**a**) kinetic energy of head, (**b**) internal energy of EAFs, and (**c**) sliding energy of EAFs. tests and subsequently validated using HIII/hemispheric drop tests, demonstrating a high level of consistency with a total CORA rating exceeding 0.93. These validated FE models were then employed in a series of simulations to assess the protective effectiveness of the EAFs in mitigating fall-related head injuries. Specifically, in the accident reconstruction scenario, the use of Igelkott Floor, Kradal, SmartCells and OmniSports resulted in a 77%, 67%, 87%, 58% reduction in the HIC, a 28%, 8%, 4%, 20% reduction in the PAV of the head center of gravity, a 41%, 12%, 66%, 10% reduction in the VMS of the skull, and a 32%, 15%, 11%, 17% reduction in MPS within the brain tissue, respectively. Among the EAFs, SmartCells provided the largest reduction in G-max and resulted in the lowest skull fracture risk, around 45.6%. On the other hand, Igelkott Floor provided the largest reduction in PAV and resulted in the lowest concussion risk of around 37.5%. Kradal and OmniSports exhibited similar behavior in terms of head kinematics and energy absorption. We did not find a strong association between brain strain reduction and contact force decrease. It has previously been found that large contact forces cause high stresses in the skull with an associated higher risk of skull fractures, while the human brain is more sensitive to large strains due to rotational loading [47]. The brain injury risk was calculated based on previously developed risk curves based on concussions in sports [50; 51]. SmartCells has the highest attenuation in G-max under high-velocity impact and a similar capability for MPS reduction as Kradal. Igelkott Floor ranks second in terms of G-max attenuation and shows the largest reduction in MPS. These observations are primarily influenced by the energy-absorbing mechanisms of different structures and materials. Generally, floors with greater thickness and lower surface stiffness tend to undergo greater deformation upon impact, leading to increased contact area and contact time. Meanwhile, the different end constraints of the columns (fixed-fixed for thin spikes and fixed-sliding for hollow cylinders) also contribute to the buckling deformation [56]. For a column or spike, which can be considered as a single energy-absorbing unit inside the SmartCells and the Igelkott Floor, its axial stress during buckling depends on the cross-sectional area and effective length. The latter structural unit, due to being composed of a multitude of slender spikes, has more buckling in various directions and thus influences the head rotational kinematics in angular impact, which is associated with less brain tissue strain and better reduction of concussion risk. This study focuses on head injuries, but other injuries, such as hip fractures, are equally common in fall incidents.