There are two types of flat feet, rigid and flexible. Rigid flat feet are feet that have no arches regardless of if the person is standing or sitting (so whether there is weight put on the feet). Rigid flat feet most often become prevalent through the teenage years and will worsen with age. Symptoms include pain in the feet and difficulty with moving the feet up or down, and side to side. The difference between rigid flat feet and flexible flat feet is that flexible flat feet are flat when weight is being put on the feet (i.e. when the person is standing) but an arch is present if the foot is not weight bearing. Flexible flat feet are much more common than rigid flat feet and are even considered to be a variation of a normal foot as the joints and muscles still tend to function properly.