Overpronation has become the most abused as well as misinterpreted lingo in running and health professional groups, specifically when it involves the designing of running shoes. The main typical model of the design of different running shoes are based on the thought of the normal or neutral posture of the feet. Pronation occurs when the feet tilts inwards at the rearfoot and the arch collapses. Supination occurs when the foot rolls outwards at the rearfoot and the arch height rises. These are typically normal healthy motions that are required for normal function of the feet. It is how the foot adapts to uneven surfaces and absorbs shock. There's nothing problematic with the motions of pronation or supination.
The phrase Overpronation is used to infer if there is too much pronation. The reason that it becomes an issue is that overpronation is supposed to be a risk factor for numerous different overuse injuries. For that reason, running shoes have design characteristics within them which are supposed to help control this overpronation. These types of design features include medial heel posts, dual density midsoles in addition to rigid heel counters. These shoes should be prescribed for those that overpronate. Runners who don't overpronate should use shock absorbing neutral footwear.
The issue with this principle is that the phrase is misunderstood significantly. There's no consensus regarding the cut-off stage between normal pronation and overpronation. There is minimal research connecting overpronation to overuse injury and if there is any, it is suggesting that it is only a small risk factor. Plenty of runners overpronate severely and don't have issues. Likewise, there are many runners which do not overpronate that have plenty of issues. Due to this confusion, there has been a recent improvement in the use of the name and the comprehension of overpronation in relationship to overuse injury and the prescription of running shoes.