The deformation of the floor above a vehicle attacked by an improvised explosive device transmits a high-rate, primarily axial, load to the lower limb of the occupants resulting in intra-articular, difficult-to-treat fractures of the foot and ankle. The aim of this thesis was to improve understanding of the biomechanics of the foot and ankle during this incident as a first step towards better design of efficient mitigation strategies. Due to the great potential of computational methods, the aim was achieved by developing and using a finite element model.

A great challenge in developing FE models of biological systems regards the selection of appropriate material properties for biological tissues. The material properties of the heel fat pad are critical for the response of an FE model of the foot and ankle and yet ill-understood for high loading rates. The first objective of this thesis was to characterise the material behaviour of the heel fat pad across strain rates. This was achieved by importing data from tests performed on cadaveric heels to an inverse FE optimisation algorithm that was developed and used to quantify the non-linearly viscoelastic material properties of the tissue.

An FE model of the foot and ankle was developed in this study to simulate high rate axial loading based on scans of a cadaveric specimen. The biofidelity of the response of the model was assessed against experimental data from various non-catastrophic tests;​ the good agreement between experimental and computational results allowed for a thorough analysis of the kinetic and kinematic response of all tissues which have allowed for a better understanding of the biomechanics of the foot and ankle in underbody blast. These findings offer an insight into the incident and can be used to facilitate the design of protective equipment and develop new ideas for mitigation strategies.