Stability running shoes have long been prescribed to control overpronation—the natural inward roll of your foot as you land and transition to toe-off. But stability shoes don’t control your foot. Instead, they ensure you have a stable platform under your foot.
Many popular stability running shoes use a medial post to achieve the stable feel. The medial post is a firmer piece of foam or plastic situated on the instep of the shoe that keeps the shoe from compressing too much.
Without a post, runners who overpronate can wear out the medial side (instep) of the shoe before the lateral side (outside), which leads to an uneven shoe that slopes inward and creates an unstable platform.