ARM END-POINT TRAJECTORIES UNDER NORMAL AND MICROGRAVITY ENVIRONMENTS

The purpose of the present experiment was to study the way in which th e CNS represents gravitational force during vertical arm pointing move ments. Movements in upward and downward directions were executed by tw o cosmonauts in normal-gravity and weightlessness. Analyses focused up on finger kinematics in the sagittal plane. In normal-gravity, downwar d direction movements showed smaller curvatures and greater relative t imes to peak velocity (AT/MT) when compared with upward direction move ments. Data from the weightlessness experiments showed that whilst dow nward movements decreased their curvature during space flight, curvatu res of upward movements changed slightly. Furthermore, AT/MT was modif ied during the first days in micro-gravity for both directions, recove ring, however, to pre-flight values after 18 days in space. Results fr om the present study, provide evidence that gravitational force is cen trally treated constituting an important component of the motor plan f or vertical arm movements. (C) 1998 Elsevier Science Ltd. All rights r eserved.