Sensorimotor reconditioning during and after spaceflight.

Exposure to microgravity drives adaptive changes in healthy individuals reconditioned for abnormal gravity states. These changes are maladaptive for return to earth's gravity. The intersubject variability of sensorimotor decrements is striking, although poorly understood. Multisensory integration, which is important for resolving sensory ambiguity on earth, is a critical mechanism for sensorimotor adaptation during and following space flight. The removal of gravitational loading also has profound effects that both negatively impact sensorimotor function and reduce capacity to overcome sensorimotor deficits. Countermeasure strategies include preflight training to facilitate transition to microgravity, pharmaceuticals and restriction of some activities early on orbit, and inflight exercise to minimize deconditioning during longer duration missions. Active motion is important to promote reconditioning upon return to earth's gravity. A supervised reconditioning program utilizes exercises that challenge multisensory integration with an increasing level of difficulty customized to the individual's state of recovery. This program also serves to increase crew self-awareness of fall risk. New resistive and aerobic exercise capabilities onboard the International Space Station contribute to improved postflight mobility. Lessons learned from inflight and postflight reconditioning programs have implications for future exploration crews that will operate more autonomously, as well as rehabilitation in clinical populations on earth.