 During the experiments, subjects will jump in different gravity fields while submitted to an additional pull-down force equal to 0-100 of their body weight on Earth. During the takeoff and landing phases of the jumps, the ground reaction force will be recorded by a force-platform, the movements of the limb segments will be recorded by means of a high-speed camera and the electrical activity EMG of the main lower limb muscles will be recorded by means of surface electrodes. 