Bed RestExerciseExercise TestResistance TrainingPhysical ExertionHead-Down TiltWeightlessness SimulationExercise TherapyRestWeightlessness CountermeasuresExercise ToleranceCardiovascular DeconditioningSpace FlightBedsWeightlessnessMuscle, SkeletalOxygen ConsumptionOrthostatic IntolerancePhysical EnduranceLower Body Negative PressureHeart RateTime FactorsPhysical FitnessPlasma VolumeBicyclingSupine PositionLegBlood PressureMuscular AtrophyBed OccupancyRegional Blood FlowEarly AmbulationWeight LiftingRunningQuadriceps MusclePulmonary Gas ExchangeCardiac OutputAnaerobic ThresholdLactic AcidHypotension, OrthostaticAdaptation, PhysiologicalMuscle Stretching ExercisesPhysical Education and TrainingKneeSweatingHemodynamicsHypovolemiaEnergy MetabolismMuscle ContractionAmino Acids, EssentialIsometric ContractionImmobilizationMuscle StrengthAnalysis of VarianceTreatment OutcomeVascular CapacitanceStroke VolumeBreathing ExercisesVibrationVascular Resistance