Pieces of apparel, such as foot-receiving devices (e.g., shoes, socks, or the like), form systems and perform methods for applying stimulus to at least a portion of a subject's body to dynamically and/or reflexively affect the subject's performance, motion, orientation, balance, timing, or the like. Such systems and methods may include or utilize: a piece of apparel, e.g., for applying the stimulus to a portion of the subject's body; an input that receives information relating to a first parameter associated with the subject's performance, motion, orientation, balance, timing, or the like; and a stimulator device that applies the stimulus to the subject's body located in or adjacent to the piece of apparel based on the first parameter. The systems and methods further may include a sensor that senses the first parameter and provides information to the system.