Artificial gravity during spaceflight prevents gait and performance deficits in a gravity-dose dependent manner

Long-term adaptations to spaceflight outside of low earth orbit (LEO), during deep space transit, and readaptations to partial gravity environments upon reaching a destination, are unclear. The combined effect of these adaptations to the LEO environment can result in declines in mobility and balance in astronauts during and after spaceflight. This study aimed to determine if there is a gravity threshold that protects from deficits in gait and performance. To do so, we exposed mice to four gravitational loading conditions (µg; 0.33 g; 0.67 g; and 1 g), induced by centrifugation, relative to preflight measurements after a 32-day mission to the ISS. Pre-flight and post-flight gait measurements were conducted utilizing a portable gait analysis system (DigiGait, Mouse Specifics, Inc). No differences were observed in gait characteristics within the Control groups (Ground Control (GC) housed in identical conditions as FLIGHT and Vivarium (VIV) housed in standard rodent cages) from initial to final gait assessment. In contrast, significant changes in gait patterns were observed in the hind limbs and the forelimbs of the FLIGHT mice after 32 days in orbit, and between groups. Continuous exposure to 1 g via centrifugation preserved gait patterns relative to both preflight and controls. Gait patterns were preserved in a gravity-dose dependent manner; with major differences observed after 0.33 g that were then attenuated / normal at 0.67 g and normal at 1 g. Notably, mice exposed to µg could not perform (locomote linearly) at live animal return, with only 50 % able to perform in the 0.33g-exposed group. As we plan for missions to the reduced gravity environments of Moon and Mars, there is a critical need to characterize these neuromotor deficits in the microgravity and partial gravity environments, and to determine whether a g-threshold exists to better mitigate the risks associated with long-duration spaceflight both in transit and upon reaching a destination.