1Chapter 19Chapter 19Factors Affecting PerformanceFactors Affecting Performancepp.393pp.393--397397Fatigue Fatigue Inability to maintain a power output or Inability to maintain a power output or force during repeated muscle contractionsforce during repeated muscle contractionsDifferent causes of fatigueDifferent causes of fatigue––400 m400 m––marathonmarathonSites of FatigueSites of FatigueCentral fatigueCentral fatiguePeripheral fatiguePeripheral fatigue––Neural factorsNeural factors––Mechanical factorsMechanical factors––Energetics of Energetics of contractioncontractionFig 19.2Fatigue Fatigue Central Central PeripheralPeripheral––Neural factorsNeural factors––Mechanical factorsMechanical factors––EnergeticsEnergeticsof contractionof contractionCentral FatigueCentral FatigueIf:If:––Reduction in motor units activatedReduction in motor units activated––Reduction in motor unit firing frequencyReduction in motor unit firing frequencyAlteration of fatigueAlteration of fatigue––MotivationalMotivational––Arousal factorsArousal factors––Psychological setting of upper limit of strengthPsychological setting of upper limit of strengthPeripheral FatiguePeripheral FatiguellNeural Factors: Neural Factors: ––Neuromuscular junctionNeuromuscular junctionAction potential appears to reach junctionAction potential appears to reach junction––Even under conditions of fatigueEven under conditions of fatigueProbably not site of fatigueProbably not site of fatigue2Peripheral FatiguePeripheral FatigueNeural Factors:Neural Factors:––Sarcolemma and Transverse TubulesSarcolemma and Transverse TubulesDepolarization, shift in ionsDepolarization, shift in ionsNaNa++/K/K++pump canpump can’’t keep upt keep up––KK++moves out with depolarizationmoves out with depolarizationAltered TAltered T--tubule functiontubule functionCaCa++++release affectedrelease affectedPeripheral FatiguePeripheral FatigueMechanical Factors:Mechanical Factors:––Reduction in cross bridge forceReduction in cross bridge force––HH++buildup may interfere with Cabuildup may interfere with Ca2+2+binding to binding to troponintroponinPeripheral FatiguePeripheral FatigueEnergeticsEnergeticsof contraction:of contraction:––Mismatch between rate of ATP production Mismatch between rate of ATP production and utilizationand utilization––Muscle fiber recruitmentMuscle fiber recruitmentType I Type I →→Type Type IIaIIa→→Type Type IIxIIxResults in increased lactate productionResults in increased lactate production––Higher PHigher Piiconcentration related to lower force concentration related to lower force Muscle Fiber Type RecruitmentMuscle Fiber Type RecruitmentFig