This is an actual computer test of a runner taken at one of our marathon expos, shown at about 1/30th the normal speed. It demonstrates the “balance and stability” of the foot in motion.
This foot belongs to a high arched supinator—who still pronates as he steps across a pressure plate designed to capture the forces generated against the ground, first in the barefoot mode, then with the individuals own "traditional" orthotic and lastly, wearing a prescriptive silicone dynamic orthotic.
Every foot has a certain amount of imbalance to it (see this in the barefoot mode as colors, red is high, blue is low), that’s normal. It’s how it hold’s you up over the long run that matters (pun intended).
With the Silicone orthotic what you are seeing, is that the fluid is filling in the arch to an equilibrium state of the foot’s own natural balanced position. This is seen as that there is very little pressure under the arch. Why? ...balance.
More contact surface of the foot on the floor, yet all the important contact points of the foot are also making contact and are stable on the floor. All the joints are in better “functional” balance, muscles are “tracking” with better efficiency.
Hydrodynamic pressure pushes the structure of the foot into its most efficient, individual natural biomechanical/alignment position— at equilibrium.