Fig. 4

a Static analysis of position 4, b high-stiffness springs (10⁹ N/mm) fixing the centre of the femoral head to the ground, c localisation of the COP and the calcaneus in position 4: the femoral head was fixed to the ground and the GRF was applied to the COP, which was fixed to the ground by means of very weak springs. The COP and the calcaneus were modelled by remote points attached to the distal tibia end. The stabilisation springs are weak springs of 1 N/mm