Overpronation has become the most misused as well as misunderstood phrases in running as well as health professional communities, specially when it comes to the fitting of running shoes. The main typical model of the manufacture of various running shoes are based on the concept of the normal or neutral alignment of the foot. Pronation is when the foot rolls inwards at the ankle joint and the arch collapses. Supination happens when the feet tilts laterally at the ankle and the arch height increases. They are normal healthy movements that are needed for normal function of the foot. It is how the feet adjusts to irregular surfaces and absorbs impact. Nothing is wrong with the motions of pronation or supination.
The word overpronation is used to describe when there is excessive pronation. The reason that this is an issue is that overpronation is considered to be a risk factor for lots of different running injuries. Because of this, running shoes have got design features in them which are thought to help control this overpronation. These kinds of design characteristics include medial heel posts, dual density midsoles along with rigid heel counters. These footwear should be used by those who overpronate. Runners who tend not to overpronate should use shock absorbing neutral footwear.
The trouble with this idea is that the term is misused significantly. There is no general opinion for the cut-off position between normal pronation and overpronation. There's also very little research connecting overpronation to overuse injury and if there is any, it's showing that it is only a small risk factor. Lots of runners overpronate severely and don't have problems.