‘Overpronation’ is usually a badly used term which is often thrown around in running communities in regards to runner’s feet and the manufacture of running shoes. Pronation is a healthy normal motion that the feet go through when running and walking. Pronation is the foot rolling medially at the rearfoot and the arch of the feet flattening. The runner needs to do this to help absorb impacts. Overpronation occurs when there's allegedly a lot of pronation. There is not any consensus among gurus just how much is too much and actually if it is actually a issue or not. There are numerous runners who overpronate that never have problems.
There is a popular belief that overpronation raises the risk for injury in runners and the research is that it does, however it's only a small risk factor and several other factors go into runners having an overuse injury. Because of this presumed risk for overuse injury running shoes have been customarily produced for minor, moderate and severe overpronators. The most firm motion control shoes are designed for the most severe overpronators. Those that have no or minimal overpronation are considered to be better off in neutral or stability rather than motion control running shoes. This model for the selling of running shoes is not backed up by the research and some data is contrary to it.
Overpronation is only thought to be a problem if the forces related to it are enough to harm the tissues. In these cases foot supports are typically indicated in the short to medium term and then based on the cause of the overpronation, gait retraining and muscle rehabilitation is used in the medium to long term. Where issues also come up around the use of the name, there is also the issue that there is not just one type of overpronation. There are various causes and no one size fits all. Foot supports will work in some runners long term. Muscle rehab and gait retraining will 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.