The human foot is a remarkable structure of 26 bones and 30+ joints integral to both walking and running. The foot must be able to both flatten (pronate) and absorb the forces of the body, as well as, become rigid (supinate) in preparation for propelling us forward. This balance of mobility and stability is accomplished through the coordination of forces and muscular contractions across the ankle and foot. The "core" of the foot made up of small muscles in the arch is a key structure for optimal functioning of the foot and kinetic chain. Authors believe the absorption and production of energy during walking and running conserves energy during the gait cycle making us more efficient in our daily movements and athletic adventures.
Previous researchers have found up to 17% of the energy absorbed by the foot in stance is immediately returned to foot at push off during running (Ker et al. 1987). More recently authors have corroborated this data and reported on the energy sparing effects of our longitudinal arch (Stearne et al. Nature. 2015). Authors reported greater metabolic costs and worse running economies in runners with stiffer arch supports and orthotics. It is believed the orthotics and arch supports restricted the ability of the arch to absorb and release energy during gait cycling placing a higher metabolic demand on the runner. The orthotics likely also weaken the key intrinsic foot muscles of the arch.
Previous research has not supported the use of more expensive, customized arch supports (orthotics) on pain and injury over less expensive, off the shelf orthotics. This article calls into question the ability of these orthotics and inserts to improve running economy and performance. Runners are advised to choose a comfortable, self selected running shoe and avoid expensive inserts.