‘Overpronation’ is really a bad phrase which is frequently tossed about in running communities when it comes to runner’s feet and the design of running shoes. Pronation is a natural normal movement that the feet go through when running and walking. Pronation is the foot rolling inwards at the rearfoot and the mid-foot of the foot lowering. The body needs to do this to help adapt to shock. Overpronation happens when there's seemingly too much of the pronation. There is not any agreement between experts just how much is too much and even if it is indeed a issue or not. There are many runners who overpronate that do not have any issues.
It is a popular belief that overpronation adds to the risk for overuse injury in runners and the research is that it does, but it is only a minor risk factor and several additional factors go into runners having an injury. Because of this believed risk for overuse injury running shoes are frequently produced for mild, moderate and severe overpronators. The most rigid motion control running shoes are made for the most severe overpronators. Those that have no or minimal overpronation are believed to be much better off in neutral or stability as opposed to motion control running footwear. This model for the prescription of running footwear is not backed up by the research and some research is contrary to it.
Overpronation is only considered an issue if the loads associated with it are high enough to harm the tissues. In these cases foot orthotics usually are suggested for the short to medium term after which based on the reason for the overpronation, gait retraining as well as muscle therapy is required in the medium to long term. Where problems also arise around the use of the term, there is also the problem that there is not just one cause of overpronation. There are several causes and no one size fits all. Foot orthotics will work in some runners long term. Muscle rehabilitation and gait retraining may work in the long term in others. For this reason you should figure out the main cause to start with and target the intervention at that.