Background and Purpose. The purpose of this study was to investigate the effects of prolonged practice of a simple motor task (a fast, unidirectional single-joint movement) on different indexes of motor performance in individuals with Down syndrome. Subjects. Eight individuals with Down syndrome were tested before and after practice involving 1,100 movements. Methods. The test consisted of three series of elbow flexion movements. In the first series, the subjects were asked to move 'as fast as possible' over four distances. In the second series, the subjects moved over one distance at a 'comfortable speed.' The initial position of the elbow joint for these two series of movements was 55 degrees into flexion (full elbow extension equals 0-degree). In the third series, the subjects were also asked to move 'as fast as possible' over two distances, but from another initial elbow position (73-degrees into flexion). Results. After training over a 2-week period, all subjects improved their performance on all tasks as reflected by both kinematic and electromyographic data. In particular, they increased the quantity of the agonist activity, decreased the antagonist onset latency, and doubled their peak velocity. They were able to transfer the improvement in their performance to the nontrained distances and to the different starting position. Subjects decreased their movement time by proportionally decreasing both the acceleration and deceleration times. Conclusion and Discussion. This study supports the idea that subjects with Down syndrome can use patterns of muscle activation that are qualitatively indistinguishable from those used by individuals who are neurologically normal. With appropriate training, individuals with Down syndrome achieved similar levels of motor performance to that decribed in the literature for individuals who are neurologically normal.741110001012