The aim of the present experiment was twofold: (a) document the developmental course of postural responses to stance perturbations causing backward body sway and (b) investigate the plasticity of these responses by assessing the changes occurring in their organization as a result of gymnastics training. Fourteen untrained children (7 to 10 and 11 to 16 years old) and 15 age-matched gymnasts were tested on a movable platform. Four conditions were used: two-legged vs. one-legged stance x vision absent vs. present. Effects of age and training were assessed on the response latencies of eight muscles. Results showed no significant effect of age, but both stance and visual conditions affected the untrained subjects' response latencies. Wee found a significant effect of training on the response latency for the upper body muscles located on the frontal aspect of the body. This effect reflects an increase in gymnasts' response latencies as compared with controls'. Stance, but not vision, affected the responses of the trained subjects. Some implications of these results are discussed.