Overpronation is when the foot collapses inward, or downward. It's also commonly known as flat feet. It's most often caused by genetics. Some people are born with high arches, while some are born with lower arches. It's also caused by carrying excessive weight, such as being overweight, or multiple pregnancies. Another cause is exercise where your foot strikes the ground for a long period of time, such as running or long-distance backpacking.