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Factors Affecting Performance

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Factors Affecting Performance

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  1. Factors Affecting Performance

  2. Factors Affecting Performance

  3. Sites of Fatigue • Central fatigue • Peripheral fatigue • Neural factors • Mechanical factors • Energetics of contraction

  4. Central Fatigue • Reduction in motor units activated • Reduction in motor unit firing frequency • Central nervous system arousal can alter the state of fatigue • By facilitating motor unit recruitment

  5. Peripheral Fatigue:Neural Factors • Neuromuscular junction • Not a site for fatigue • Sarcolemma and transverse tubules • Ability of muscle membrane to conduct and action potential • Repeated stimulation of sarcolemma can reduce size and frequency of action potentials • An action potential block in the T-tubules • Reduction in Ca++ release from sarcoplasmic reticulum

  6. Peripheral Fatigue:Mechanical Factors • Reduction in force per cross bridge • Reduction of force generated at a given Ca++ concentration • H+ interference with Ca++ binding to troponin • Inhibition of Ca++ release from SR • Lack of ATP to dissociate the cross-bridge from actin

  7. Peripheral Fatigue:Energetics of Contraction • Mismatch between rate of ATP production and utilization • Fatigue results in slowing of ATP utilization to preserve homeostasis • Muscle fiber recruitment in increasing intensities of exercise • Type I  Type IIa  Type IIb • Progression from most to least oxidative fiber type • Results in increased lactate production

  8. Pattern of Muscle Fiber Recruitment

  9. Ultra Short-Term Performance • < 10 seconds • Dependent of recruitment of Type II muscle fibers • Generate great forces that are needed • Motivation, skill, and arousal • Primary energy source • Anaerobic • Phosphocreatine

  10. Ultra Short-Term Performance

  11. Short-Term Performance • 10-180 seconds • Shift from anaerobic to aerobic metabolism • 70% energy supplied anaerobically at 10s • 60% supplied aerobically at 180s • Primary energy source • Anaerobic glycolysis

  12. Short-Term Performance

  13. Moderate-Length Performance • 3-20 minutes • Increasing reliance on aerobic energy production • 60% ATP generated aerobically at 3 min • 90% ATP supplied aerobically at 20 min • Requires energy expenditure near VO2max • Type II fibers recruited • High levels of lactate • Factors that interfere with O2 delivery are limiting • Altitude, anemia

  14. Moderate-Length Performance

  15. Intermediate-Length Performance • 21-60 minutes • Predominantly aerobic • Usually conducted at less than 90% VO2max • Environmental factors are important • Heat • Humidity • State of hydration

  16. Intermediate-Length Performance

  17. Long-Term Performance • 1-4 hours • Environmental factors important • Ability to deal with heat and humidity • Muscle and liver glycogen • Maintain rate of carbohydrate utilization • Diet and fluid ingestion influence performance

  18. Long-Term Performance