The foot has a complex anatomy designed to bear the weight of the body and to propel the body forward in walking and running. The talus or ankle bone sits in the ankle mortise and is the top link of the main longitudinal arch of the foot. The longitudinal or medial arch is the largest and is on the inside of the foot, absorbing the loads in standing postures and aided in its elastic recoil by the spring ligament. The outside of the foot has a smaller arch known as the lateral arch and the front of the foot has a transverse (across) arch between the first and fifth metatarsal heads.
The foot arches have a very important role in the function of the foot and without them it would not be the dynamic propulsion system that it is. They absorb the energy and forces involved when body weight is applied to the ground, store it to some degree and release it as the next step is taken. If you watch someone walk with very flat feet and no spring you will be struck by the lack of dynamic movement, the slowness of gait and the lack of balance. Maintaining the health of the foot arches should be an important part of keeping fit and able as we age.
There are two main functions the foot is required to perform: managing the forces generated by the body weight, often magnified by motion, and to absorb and create the propulsion energies needed for gait. The calf muscles reviewed in another article about the ankle contribute towards the maintenance of the foot arches but this is also aided by the toe muscles. The toe long flexor muscles begin in the calf, running under the sole of the foot down to the toes, functioning to grip the ground or curl the toes. The shorter muscles to the toes, having their origin in the feet, are called the intrinsic muscles and function by pulling the toes down onto the ground without any flexion occurring.
In normal gait when the foot hits the ground the heel will hit the surface initially and somewhat on the outside. As the leg rolls over the ankle the talus slides inside the mortise of the ankle and the arches start to bear weight and their ligaments and joints absorb forces. As the step continues the weight moves inwards and forwards to end up on the metatarsal heads of the first and second toes, with the final push off coming from the toe flexor muscles.
Each moving joint in our body has a degree of accessory movements in it, which are limited and subtle internal movements between joint surfaces which cannot be exhibited in isolation. A normal joint depends to some degree on the accessory movements present within the joint and if these are lost or reduced the joint''s function is compromised. A high number of intricately designed foot bones are packed into a small area, creating the arches, and all these bones have highly functional accessory movements between them.
As the body weight starts to be borne on the foot the arches begin to suffer a flattening effect which is countered by the calf and toe muscle strength and the ligamentous elasticity and tension. As the gait cycle approaches the push off point the arches are supported against the weight by the toes gripping the ground, the energetic ligament recoil and the muscular sling support provided by the calf muscles. As walking proceeds the arches heighten and lower in a cyclical movement during which the complex multiple joint complexes of the arches exhibit continual accessory movement between all the bones.
Each bone of the foot needs to have the ability of independent movement relative to the others, with weight causing the underneath of the joints to open as the upper surfaces close. The individual ability to accommodate to the surfaces which present themselves is vital, allowing the foot to adjust to the dynamic circumstances required. Losing some of the range of accessory movement makes the foot lose some of its dynamic flexibility as it changes into a more static body weight prop from the active organ of propulsion.