EFFECT OF WEIGHTLESSNESS ON POSTURE AND MOVEMENT CONTROL DURING A WHOLE-BODY REACHING TASK

Here are reported preliminary results of the ''Synergy'' experiment pe rformed aboard the Russian orbital station ''MIR'' in July 1993 (Altai r Mission), The experiment was carried out before, during, and after t he space flight of two astronauts (S1 and S2). The duration of the fli ght was 21 days for S1 and 6 month for S2, The subjects were tested du ring preflight, inflight and postflight, The astronaut subjects were f ixed on the ground by the feet. They were asked to pick up a box in fr ont of them on the ground. Two velocities of movement and two distance s of the target to be reached were tested, The movement of several sma ll markers placed on the body was recorded on video tape. Results show that the shape of head and hand trajectories in the sagittal plane re mains roughly the same during the flight in spite of the modification of mechanical constraints, Trajectory invariance does not result in jo int angular displacement invariance, These data indicate that the plan ning of the movement takes place in terms of head and hand trajectorie s rather than joint rotations as it was previously suggested for simpl e arm reaching movement.