The static and dynamic forces operating in the foot relate to the weight of the body and the reactions from muscular contraction necessary for balance, movement and adaptation to the nature of the ground surface. Classically, forces are described as operating through two arch systems: the internal, which centres around the first metatarsal, and the outer, which operates through the fifth metatarsal. According to Pietrogrande (1965), the talus is the receiver, transmitter and distributor of these forces along two systems, posteriorly distributed towards the calcaneum, anteriorly through both internal and external pillars of the forefoot and above to the tibia. The magnitude of forces is increased when the foot is dorsiflexed or plantarflexed at the ankle joint. However, there is reason to believe that the distribution is not as simple as this description indicates. Tensile and compressive forces balance across different transmission systems of the foot, which may be likened to an aeroplane in flight rather than a car on the road; there is pitch, roll and yaw.
