The DFA System is useful for persons exhibiting or potentially developing calf muscle contractures. There are two product configurations: a Sleep System for overnight or nap wear, and a Gait System for use in gait training. You can also purchase a Combo unit for full-time use: the Combo unit contains one each of both the Sleep and Gait Systems. Product size is determined by the wearer’s shoe size (see Sizing tab below for information.)