While recent findings demonstrated the importance of initial state estimates about gravity for optimized motor control, it remains unclear whether novel initial states are rapidly implemented movement planning (and control) in the same way when gravity is removed or increased. Here, we investigated the effect of microgravity and hypergravity exposure on whole-body reaching movements performed by standing subjects during parabolic flights. Reaching movements were analyzed regarding spatial accuracy (finger endpoint deviation), arm kinematics (arm angular displacement), whole-body kinematics (body bending) and EMG activity (muscular activation and synergies) of eight muscles. Results showed that kinematics and muscular activity are adjusted in microgravity allowing accurate whole-body reaching, thus confirming the perfectly scaled sensorimotor reorganization reported in previous recent studies. Contrasting with these observations, participants hardly reached the targets in 1.8g (systematic undershot). Strikingly, whole-body kinematics remained unchanged in hypergravity compared to 1g observations. Finally, while the analysis of synergies highlighted a comparable muscular organization in all gravitational contexts, our main findings revealed local muscular adjustments leading to accurate motor responses in microgravity, but not in hypergravity.
Performance During Whole Body Reaching Movements Is Impaired In Hypergravity While Preserved In Microgravity
