 If investigators know that the anticipatory mechanisms involved in precision grip take into account the gravity, however it is unclear how they adapt to changes in the gravitational level. The objectives of this study are to study and model the movement control and the mechanisms underlying learning and adapting to the condition of weightlessness. Specifically, i investigators will determine if a change in the level of gravity is taken into account when controlling grip force and ii investigators will examine the effects of gravity change on hand-eye coordination. 