Isometric ContractionMuscle ContractionMuscle FatigueMuscle, SkeletalElectromyographyIsotonic ContractionTorqueElbowRecruitment, NeurophysiologicalMusclesElectric StimulationMuscle Fibers, SkeletalKneeMyocardial ContractionMotor NeuronsMuscle StrengthUterine ContractionSarcomeresMusculoskeletal Physiological PhenomenaMuscle RelaxationBiomechanical PhenomenaPhysical EnduranceMuscle, SmoothMyosinsPsoas MusclesVolitionQuadriceps MuscleTime FactorsPapillary MusclesPhysical ExertionCalciumRana temporariaVasoconstrictionAnkle JointMyographyPhosphocreatineThighStress, MechanicalElasticityMuscle SpindlesRana esculentaMyofibrilsRabbitsMuscle, Smooth, VascularLegPhenylephrineEvoked Potentials, MotorMuscle Strength DynamometerFingersPotassium ChlorideTendonsAnuraHandAction PotentialsAdenosine TriphosphateMotor CortexForearmHand StrengthExerciseThumbKnee JointElbow JointDose-Response Relationship, DrugGuinea PigsArmReflex, StretchWeight-BearingAcetylcholineCatsFemoral NerveVasoconstrictor AgentsModels, BiologicalAorta, ThoracicMovementMyosin Light ChainsNorepinephrineTracheaMasseter MuscleRats, WistarFeedback, SensoryHindlimbNeural ConductionBupranololAnalysis of VarianceTranscranial Magnetic StimulationAdaptation, PhysiologicalEnergy MetabolismHeart RateRats, Sprague-DawleyAgingReflexFootMuscle WeaknessBlood PressureCreatineActinsRana pipiensDogsAnkleTask Performance and Analysis