The arch is absent and the whole sole rests on the ground. Everyone is born with flat feet; in some suffering from this condition, the ligaments are weak and do not develop properly to form an arch. Some people suffer from fallen arches where the ligaments weaken in adult life, often from rapid weight gain or neurological or muscular ailments.
The signs of flat feet are over pronation, an abnormality in the normal gait cycle (mechanics of the foot movement) since the arch collapses during impact activities such as walking, standing or running. An additional sign is foot and heel pain caused by plantar fasciitis, in this case it results in being overly stressed due to elongation from the flat arch.
Often whilst examining the heels of your shoes, you will notice that the heel is worn down on one side, either the outside or the inside. This process is called pronation, and as the ankle hits the ground it either rolls outward, or rolls inward. Not only is this process ruining shoes but left unchecked it will continue to get worse even resulting in a limp and causing improper body limb alignment.