The Provision 4 exemplifies the evolution of technical support in running shoes. It is a completely updated and overhauled version of the previous models and is at the forefron of natural biomechanical advances. In addition to a medial GuideRail, we've developed a new arch feature, unique to Altra which uses proprioception to help slow pronation and neutralize your step cycle. This feature is a new, revolutionary way of offering support only when you need it without interrupting your natural stride. Every type or runner will love this fresh approach to guided, natural foot movement.