Walking on the moon: hypogravity drives the emergence of a proprioception-dependent locomotor state

Animals must adapt locomotion to changing environments, but how the nervous system flexibly select gait remains unclear. Gravity is a powerful natural perturbation altering body loading and limb dynamics. Apollo astronauts often skipped on the Moon, adopting an asymmetric gait rarely used on Earth, yet the motor control basis of this behavior is unknown. Here, by studying the effect of hypogravity on locomotion in humans and mice, we identify a conserved strategy for gait adaptation. Muscle synergy analysis in humans shows that skipping in reduced gravity is generated through flexible reuse of existing motor modules rather than construction of new ones. In mice, lunar gravity elicited a skipping-like asymmetric gait and genetic elimination of muscle proprioceptors abolished it. Thus, hypogravity reveals a proprioception-dependent mechanism for flexible gait selection.