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The Human Foot
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.
The foot is designed to fulfil two main actions: to accept the forces generated in locomotion and generate propulsive forces to effect gait and to manage the forces involved in movement of the body weight which are often greatly increased by motion. Some of the calf muscles, as mentioned in an ankle article recently, function to keep the arches of the feet working but the long flexor muscles of the toes do this also. Originating from the calf and running underneath the foot to insert into the toes, these muscles bend the toes and work by gripping the ground for stability and movement. The shorter intrinsic muscles, originating in the feet and inserting in the toes, bend the toes whilst keeping them straight.
If the foot hits the ground in a person with a highly functional foot the heel will contact the surface first and slightly on the lateral side. The foot rolls forward as the talus rocks inside the ankle mortise and weight begins to be taken by the arches with the joints and ligaments absorbing the stresses. The weight transfers gradually over to the inside and through the first and second metatarsal heads until the foot pushes off partly with the power of the toes 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.
The individual foot bones need to be able to all move independently, opening out underneath as the pressure is applied and closing up in the upper surfaces. The bones must be able to adjust themselves as the foot spreads to accommodate itself to the surface, allowing a dynamic readjustment to constant changing ground conditions. If some of the accessory movement range is lost the foot loses some of its plastic adaptability as it becomes a rigid prop for bearing body weight and gives up its comfortable propulsive role.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, physiotherapists in Solihull, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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Filed under back pain by on Dec 26th, 2009. 
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