Fig. 7

Strain distribution maps of the stiffening element during bending: (a) The strain map for Frame 1 shows diffused strain distribution throughout the structure, with relatively low strain near the heel and toe regions. This diffused strain suggests that deformation is more evenly distributed across the stiffening element in this intermediate bending stage; (b) The strain map for Frame 2 reveals more localized strain, particularly concentrated near the metatarsophalangeal (MTP) joint, where the structure experiences significant curvature during bending in the bending frame 2. The localized strain in Frame 2 aligns with the bending of the foot during running, where the MTP joint acts as a critical point for energy transfer and propulsion. In both frames, strain remains minimal near the heel and toe, reflecting structural stability in these regions.