Human position sense and the role of gravitational torque: a parabolic flight study

Abstract An important issue in spaceflight is the loss of sensory information associated with malfunction of the proprioceptive system. Specifically, in microgravity, astronauts become uncertain about the positions of their limbs if they cannot see them. We have recently been studying limb position sense during altered gravity conditions and demonstrated that this becomes degraded, most probably because of the changed gravitational torque at limb joints. To further examine this assumption, a one-arm pointing study was conducted to investigate the effects of micro- and hypergravity created during parabolic flight. Results of six participants showed that the effects of altered gravity on position sense were particularly evident when the difference between the gravitational torque experienced under normal gravity and the torque under altered gravity was large. This suggests that a mismatch between the internal model of gravity and incoming sensory information underlies a deterioration of the sense of position. Moreover, it was explored whether the microgravity-induced loss of torque at the elbow joint can be recovered by wearing compression garments, but results revealed no beneficial effect.