Impact shock, is defined as the force applied over a short period of time when the horse limb hits the ground. Impact shock creates destructive vibrations that travel up the lower limb. Several structures in the limb are believed to attenuate impact shock (concussion). The viscoelastic deformation of the hoof wall is considered to be the major shock damper.
Concussion is further absorbed by blood and vessels (hemodynamics/fluid dampening). Other structures that play a role are soft tissues inside the hoof (tendons and ligaments), joints and bones.
Shoeing reduces the shock absorption capacity of the hoof sending the impact shock up to bones, joints, tendons and ligaments increasing the risk of injury. The effect depends on the type of material the shoe is made off: the shock absorption properties of steel and that of aluminum are less than that of polyurethane shoes. Horses shod with regular (traditional) steel shoes experience a 15% higher concussion than unshod horses at the level of the hoof wall.
A reduced shock absorption capability of traditional shoes can be explained by the reduced heel expansion when shod with traditional one piece shoes.
Research performed on the Twin™ Shoe, clearly shows that heel movement (the key variable of hoof deformation) is not negatively affected by the Twin™ Shoe compared to the barefoot hoof, whereas a traditional shoe restricts heel movement by approximately 36%.
As such, absorption of the impact shock by the hoof and the circulation when shod with the Twin™ Shoe reduces the amount of destructive vibrations to the lower limb joints and bones, thus protecting them from damage.