 The main aims of the present project include 1 to study the longitudinal effects of whole-body vibratory exercise on bone metabolism in adolescents with and without DS and 2 to evaluate whether a low frequency vibratory training program consisting of 3 sessions per week for 9 months each vibratory session last approximately 10 minutes and includes 5-6 bouts of 1 min with 1 min rest between bouts can improve bone development in these populations. Finally, and additional aim of the project is 3 to determine how long these effects may last after the end of the intervention. 