Shear

Horizontal force on the foot that takes place during normal movement.  Shear force causes the different layers of skin in the foot to move in opposing directions, creating blisters or other lesions. Shear force is also responsible for the breakdown of the foot’s fat pads over time, as the fat pads absorb energy created when layers of skin and tissue move against the motion of the bones in the forefoot. For details, see the IPFH white paper.