Flat feet is a very common deformity of the feet and is characterised by a low medial arch, where it is either close to the ground or even touching the ground in severe cases. The arch consists of ligaments, tendons and fascia which is strong and elastic.
According to Munro BJ and Steele JR (1998), between 20% and 37% of people have pes planus to some extent. Most infants are born with flat feet from where the arch growth begins to appear around the age of three and is typically not achieved until the child is between seven and ten. Children and teenagers who have flat feet may experience cramps at night or pain in the arch of their feet. Adults may complain of pain in the midfoot, heel, lower leg, knee, hip, or back as a result of strained muscles and connective tissues. This can also have an effect on walking patterns.
Proper footwear is essential to support the foot arch to decrease the risk of injury and pain. In more severe cases when pain is present, foot orthotics and NSAIDS should be considered. Biokinetic rehabilitation of flat feet includes reducing pain, improving foot flexibility, getting weak muscles stronger, and focussing on proprioception. During this process it is important to train gait patterns, gross motor abilities, and functional activities that contribute to normal daily activities.
Examples of what you can do at home to help with your flat feet:

