 In this project, investigators propose to study the jump in different reduced gravity fields obtained during parabolic flights profiles but also during increased gravity fields obtained during turns of the airplane or during the pull-up phase of the parabola. By means of a pneumatic device, an additional pull-down force will be added to the vertical force caused by the gravity field. By combining different levels of gravity to different levels of the added pull-down force it will be possible to dissociate the respective contribution of the otolithic and proprioceptive systems to the anticipatory landing response. To the investigators knowledge, only one study has modified the gravity field during a jump. However, these authors did not add a pull-down force and only analyzed the vertical ground reaction force. 