Each of your feet consists of 26 bones, which is almost 1/3 of the bones in your body. There are 30 joints, which give the foot its mobility and 29 muscles that direct the movement of your foot. Finally, each foot contains over 100 different ligaments that connect one bone to another and hold the entire structure together. This mass of tissue and bone must serve many purposes. Perhaps the most important function is as a loose “bag of bones”, adjusting to uneven ground surfaces. But, in the same step, the foot must transform to serve as a firm support to provide a strong, stable push off the ground.
Each step begins as the foot is supinated before heel strike; this means that the outside heel touches first followed by weighting of the arch. The foot then pronates (rolls in slightly); together with contraction of the calf muscle, this will dissipate the shock to the entire foot and leg. The arch will flatten slightly until the arch ligament (plantar fascia) is tightened. During the liftoff phase the front of the foot supinates (rolls out) to stabilize the foot until the big toe leaves the ground.
Problems will occur if any of the above processes does not occur, or occurs to a greater degree than intended.
For example, once the heel touches and weights the arch, if that sequence of events is not followed by pronation and the foot remains to the outside of the foot, the foot loses its ability to absorb the shock. If the foot does not absorb this shock the vibration will work its way up the leg until the shock is absorbed by another joint; one that may not be designed to perform this duty. On the other hand, if, at the time of pronation the foot rolls too far to the inside, the foot is then out of alignment and will misalign everything above it and will be unable to lock out correctly for a strong push off of the ground.
Orthotics will aid this process by gently guiding the foot into its correct positioning throughout the time the foot is on the ground.