Flat feet is a condition in which the arch of the foot is depressed, generally making the sole of the foot completely or almost completely stay in contact with the ground. About 20-30% of the population generally has flat feet because their arch never formed during growth.
Having flat feet can sometimes make it difficult to walk due to the stress it places on the ankles. The general alignment of your legs is thrown off because the ankles move more inward which can cause some major discomfort. This also has a big effect on the knees as many people that have flat feet often have arthritis in that area. However, in many cases, having flat feet do not cause any pain and it should not be a cause for concern in that case.
For those that run, there are specific shoes to help realign the ankles with a lot more support and less pronation. The weight shifting in this activity is very quick, so that's why it's important to know if you have flat feet early on in your life, in case of injury down the road.
Symptoms of flat feet can include: pain around the heel or arch area, trouble standing on the tip toe, swelling around the inside of the ankle, flat look to one or both feet, and having your shoes feel uneven when worn. A major cause of flat feet is never having developed an arch on your foot. Overtime, a lot of stress and trauma to the foot can actually weaken the posterior tibial tendon that runs around the inside of the ankle. This is the reason why some people with flat feet have pain around that particular area.
There are a number of ways to help treat flat feet. One way is going barefoot. Studies have shown that those that grew up going barefoot or wearing less closed-toe shoes actually have more of an arch because the general strength and fullness of the arch increased. Also, those with flat feet have a weaker Achilles tendon, and exercise to the area will help stretch the area. In a lot of cases, there are great shoe inserts provided by orthopedists to provide ankle support as well as reduce the symptoms that go along with severe flat feet. For those that suffer severe pain in that area, tendon surgery is an option to help with any posterior tibial tears.