The Foot
The foot\’s design is complex and specialised to manage the forces generated by bearing the weight of the body and by the need to propel the body in gait. The talus is at the apex of the main longitudinal foot arch and is held firmly by the ankle mortise. The largest arch is the lengthways or medial arch of the foot which manages the forces involved in moving the body and standing, the spring ligament contributing to this by storing and releasing the energies involved. The outside or lateral arch is less obvious as is the transverse arch at the front of the foot.
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.
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.
The independence of movement between all the many foot bones is vital as the weight causes a spreading of the under surface of the joints and a closing in of the upper joint lines. The foot can accommodate to the circumstances which present themselves in a dynamic fashion at least partly to the individual inter-joint movements. The foot will lose some of its flexibility in responding dynamically to circumstances if accessory movement is lost and the foot changes function from an active system to a passive platform.
Jonathan Blood Smyth is the Superintendent of Physiotherapy at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for Winchester physiotherapy visit his website.
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