Agility

Agility requires flexibility and balance which depends on a stable foundation.

You have felt and seen how instability causes jerky motion.  Just ask a friend to balance on a 2x4 laying flat on the ground and take a look.  The body becomes rigid, and jerky motion causes loss of balance. 

Instability causes continuous firing of both flexors and extensors (Flexors cause motion in one direction, extensors in the opposite direction).  If both muscles are fired simultaneously, rigidity will replace flexibility and fluid motion. 

Hyperpronating feet cause constant postural instability hence there is no equilibrium between the flexors and extensors causing overuse of the postural muscles.  Hyperactive muscles are prone to trigger points causing cramps and stiffness leading to limitation of range of motion and significant pain.  Shin splints is just one classic example of what Posture Control Insoles^(TM) can eliminate.