1. A reaction movement sequence system for directing and assessing leg movement performance of a subject, comprising: a. video means; b. field means for confining subject leg movement including a plurality of intercept positions each of which comprises a pair of laterally spaced foot impact pads geometrically oriented to locate the subject frontally with respect to said video means when the subject is positioned thereon and arrayed on the field in predetermined positions to provide predetermined relationships with respect to the other pads and reachable by lateral, forward and backward movements of the subject; c. analog sensor means operatively associated with said impact pads providing a signal in accordance with changes in loading on said impact pads; d. first means operatively associated with said video means for presenting thereon a replication of said field means; e. second means operatively associated with said first means for presenting a visual cue on said replication of said field means at a target intercept position corresponding to one of said plurality of intercept positions different from the current intercept position of the subject; f. timing means for receiving said signal from said sensor means and determining (1) the time interval from said visual cue until commencement of movement by the subject for exiting said current intercept position, (2) the interval from said commencement of movement until the subject reaches said target intercept position, and (3) the time interval until said subject reaches predetermined stability on said target intercept position; g. third means for initiating another visual cue when said subject reaches said target intercept position, said third means generating subsequent visual cues in a nonpredictable fashion as to timing and prescribing a course of subject movement between said current intercept position and subsequent intercept positions; and h. means associated with said timing means and said video means for graphically presenting on said video means information related to said timing intervals.