The second it to help prevent injury by either decreasing the stress on the leg. This is thought to occur through improved impact absorption or attempting to improve the alignment of the leg through compensation for malalingnment. The third possible function is enhancement of performance. In order for proper function the foot variation must be identified. Regardless of the variation, the shoe must fit the foot and not vice versa.
Flat feet are generally excessively mobile and the foot has a tendency to move too much.
In this case, the ligaments and muscle associated with this area tend to be stressed more than normal. This person tends to have a wide forefoot and a narrow heal which makes it difficult in shoe fitting. Breakdown is most often seen on the inside of the sole which leaves the foot in an unsupported position. Shoewear should conform to the foot which will give it the support it needs to function properly. The individual with a cavus or high arch foot will generally have less motion within the joints of the foot and require more room on the top portion of the foot.