For runners exhibiting overpronation, the outside of the heel makes the initial contact with the ground, but the foot rolls inward more than 15 percent. Consequently, the ankle and foot can’t stabilize the body properly, so shock isn’t absorbed as efficiently. Along with causing foot discomfort and problems, overpronating also causes extra stress and tightness to the muscles. Severe overpronators need a lot more structure than neutral shoes have to offer in order to keep from injuring their feet and legs. These are called motion-control shoes, and they are typically the most stable kind or running shoe available. Since they use a larger, more dense medial post for stability, they are heavier and stiffer than other running shoes.