Throughout our lives, our feet must withstand considerable stress: the entire weight of the body and peak forces of up to 7 times our body weight (e.g., upon landing after a jump). The human foot is only able to cope with these stresses because it has been uniquely designed by nature in a way that resembles a Roman arch.
A normal foot has a longitudinal arch and a transverse arch, within which 26 bones are connected and stabilized by ligaments and tendons. Deviations from the ideal form (flat feet, high arches) limit the foot’s ability to bear weight.
Since tendons and ligaments can become less elastic over the course of a lifetime and more brittle with age, the shape of our feet changes and they become wider as we get older. This is evident in the fact that most people in middle age notice that they need a shoe size larger than they did in their youth. Excessive strain from sports or work, weight gain, pregnancy, etc., exacerbate this tendency.