Bed RestHead-Down TiltWeightlessness SimulationWeightlessness CountermeasuresRestCardiovascular DeconditioningSpace FlightBedsWeightlessnessOrthostatic IntoleranceLower Body Negative PressurePhotic StimulationTime FactorsBed OccupancyMuscle, SkeletalMuscular AtrophySupine PositionPlasma VolumeReaction TimeExerciseEarly AmbulationGeneralization, StimulusAcoustic StimulationHypotension, OrthostaticVibrationHypovolemiaPhysical StimulationVisual PerceptionDiscrimination LearningImmobilizationAmino Acids, EssentialVascular CapacitanceDiscrimination (Psychology)