Pronation is an active and natural shock absorbing movement of the foot. It is characterised by the foot rolls inward and the arch lowering This is a normal movement that commences immediately after the foot makes contact with the ground. Whilst it is primarily a shock absorbing movement it also allows the foot to adjust and adapt to the terrain. It is a complex movement pattern and not fully understood. Pronation is synchronised during gait so as to cause internal rotation of the leg. Key to an assessment of gait is the timing of foot pronation as well as the total amount of pronation that occurs. For example should pronation occur "too late" then this will delay external rotation of the leg during propulsion. This can contribute to injuries particularly in the knee. The velocity or speed of foot pronation is also taken into consideration. A rapid pronation velocity can place significant stress on foot and lower limb.
Determining if you pronate excessively is the topic of debate. Pronation is a neccessary shock absorbing movement however excessive pronation can be injurious. What however is excessive? The use of orthotic devices can reduce the amount of harmful pronation that occurs, and also reduce the velocity or speed of this movement. In the video clip below note the inward lean of both heels in this runner. This is just one visual reference that practitioners will use in both selecting your orthotic, or modifying your orthotic prescription during treatment.