Neurophysiological effects of partial gravity on bimanual control: A parabolic flight study

Many of the activities associated with spaceflight require individuals to use both limbs simultaneously to accomplish the task. Motor control, as well as visual performance and spatial orientation are disrupted by gravitational transitions between 1G and 0G, but very little is known about the sensorimotor deficits between 0G and 1G. The objective of this analog-based research effort is to investigate the impact of partial G-levels on bimanual coordination tasks that are operationally relevant for spaceflight. Using parabolic flight to simulate different gravity levels (0g, 0.25g, 0.5g, 0.75g, 1g), participants performed isometric force coordination tasks while electromyography (EMG) data were collected to assess neuromuscular activity. Results showed that at lower gravity levels, force production was significantly reduced, became less harmonic, and more variable, particularly during complex tasks, indicating reduced coordination stability. Additionally, EMG-EMG cross-wavelet power analysis revealed significantly lower beta-band (13–30 Hz) normalized power in 0g compared to 1g, suggesting weakened neural synchronization between limbs in the absence of gravitational loading. Partial gravity conditions partially restored both force stability and neural coupling, emphasizing the role of proprioceptive feedback in motor control. These findings highlight the importance of gravitational input for maintaining motor coordination and have practical implications for astronaut training, equipment design, and countermeasures to support performance during space missions.