Pronation is the term to describe “the motion of rotating toward the prone position (having the front or ventral surface facing downward),” as commonly defined in medical dictionaries. The term is also used to describe a slight rolling inward motion made by the foot in a normal stride. This motion accommodates movement in the foot and ankle when the heel makes contact with the ground. Rolling inward approximately fifteen percent, the foot is able to support your body weight while distributing the force of the impact. Consider it a built in shock absorber that kicks into gear before you push off from the front of your foot into the next step.
Overpronation indicates that after the heel makes initial contact, the foot is rolling inward more than the ideal fifteen percent when assessed. Underpronation signifies a rolling outward of the foot, moving more than the ideal fifteen percent in the opposite direction. Both over- and under- pronation indicate that the foot and ankle are having trouble stabilizing the body properly, and wearing the right shoes for your feet can make a significant difference.
It’s important to be fit properly by a salesperson with reasonable knowledge of the foot in order to ensure the right balance for your pronation style. Often, runners with flat feet will overpronate, where runners with high arches are more likely to underpronate. Various shoes can accommodate to encourage more natural foot motion, resulting in better support—not just for the feet and ankles, but for the whole body.