The foot has evolved to be an incredibly advanced system. The foot moves in the most efficient and healthy way, it rolls, stretches, expands, and grasps the ground. For example the foot has its own built in system for absorbing shock, the foot arch support: foot’s arch flatten on impact to dissipate shock. For stability or motion control: foot uses pronation, rolling inward, to deflect shock. When the foot enters the ground it becomes a shock absorber, and allows through chain reaction the knee, hip and trunk to become a shock absorber in all three planes of motion. It is a flexible mobile adapter, by reacting to gravity, body weight, and momentum and ground reaction forces it collapses and allows the rest of the body up the chain to eccentrically load. It turns the body on to eccentrically load to allow the body to do what it wants to, walk and jump. It represents a stable propeller that allows us to concentrically unload. The foot is initially mobile to ultimately give us the stability that we need to move and to jump. When it is stable, it becomes a rigid lever and facilitates an unloading of the kinetic chain. It needs to be flexible and mobile or stable in the right time.
The magic of the foot is its ability to quickly transform from a mobile adapter to stable propeller. Foot function is completely subconscious. What the foot does is completely reactive. We therefore must know what the foot reacts to, and how it reacts to those forces in order to functionally evaluate and heal.