There are numbers of theories that supports the biomechanical function of the foot and the use of foot of this foot orthotics by podiatrists to treat foot.  Of these theories there are some of them who do have a good evidence to support them, and there are also others who do not support. Within podiatry there is a lot of debate as to the merits of the different theories. The oldest and most established is known as Root Biomechanics. Another more recent there that is gaining popularity is known as sagittal plane facilitation theory. This is a model that is dependent on movement ahead in the sagittal plane and the theory is all about facilitating that motion.