Hindlimb SuspensionHindlimbMuscular AtrophyMuscle, SkeletalWeightlessness SimulationWeight-BearingSuspensionsMuscle Fibers, Slow-TwitchMuscle Fibers, Fast-TwitchMyosin Heavy ChainsOrgan SizeMuscle Fibers, SkeletalAtrophyMuscle ProteinsRats, Sprague-DawleyAdaptation, PhysiologicalRats, WistarMuscle ContractionBody WeightTime FactorsRNA, MessengerIschemia