Evaluation of theories of complex movement planning in different levels of gravity

Due to high redundancy of degrees of freedom in the human body, we can perform any movement, from the simplest to the most complex, in many different ways. Several studies are still trying to identify the motor strategies that master this redundancy and generate the movements whose characteristics are highly stereotyped. The aim of this work is to build a simulator that is able to evaluate different motor planning hypotheses. The most interesting applications of this tool occur in studies of the motor strategy in microgravity conditions. The comparison between simulated movements and kinematics data recorded both on Earth, and during a 5-month mission on board the Mir station shows that for a complex whole-body movement (such as trunk bending) a single planning criterion cannot explain all movement aspects. However, the simulator allows an understanding of the motor planning adaptation of astronauts. In space, the lack of equilibrium constraint (which on Earth brings about the center of mass control) leads to a new motor strategy that minimizes dynamic interactions with the floor. © 2005 Elsevier Ltd. All rights reserved.