How does microgravity affect the muscular and kinematic synergies in a complex movement?

The planning and the execution of voluntary movement relies on sensorimotor transformations in which representations of the external environment are integrated into motor programs. We studied executions of Whole Body Pointing movements, in normal and in transient microgravity (parabolic flights) conditions. Three processes could lead to adaptation to the new environmental condition: a radical change of terrestrial synergies, their partial modification or preservation. By applying a multivariate analysis on kinematic and electromyographic (EMG) data and by comparing the 1g and 0g conditions, our findings hint the hypothesis the descending information from vestibular system may be directed to change the synergies' modulation. An analogous analysis was performed on the kinematics: the invariance of intersegmental coordination among the segments' elevation angles suggests that these kinematic waveforms are used as reference signals to determine the appropriate muscle synergies in a subordinate and flexible manner in order to adapt to the novel mechanical constraints.