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Chapter 19 Factors Affecting Performance

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  1. Chapter 19Factors Affecting Performance EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley Presentation revised and updated by Brian B. Parr, Ph.D. University of South Carolina Aiken © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  2. Objectives • Identify factors affecting maximal performance. • Provide evidence for and against the central nervous system being a site of fatigue. • Identify potential neural factors in the periphery that may be linked to fatigue. • Explain the role of cross-bridge cycling in fatigue. • Summarize the evidence on the order of recruitment of muscle fibers with increasing intensities of activity, and the type of metabolism upon which each is dependent. © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  3. Objectives • Describe the factors limiting performance in all-out activities lasting less than ten seconds. • Describe the factors limiting performance in all-out activities lasting 10 to 180 seconds. • Discuss the subtle changes in the factors affecting optimal performance as the duration of maximal performance increase from three minutes to four hours. © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  4. Factors Affecting Performance Figure 19.1 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  5. Sites of Fatigue • Fatigue • Inability to maintain power output or force during repeated muscle contractions • Central fatigue • Central nervous system • Peripheral fatigue • Neural factors • Mechanical factors • Energetics of contraction © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  6. Possible Sites of Fatigue Figure 19.2 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  7. 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 • Increasing motivation • Physical or mental diversion • Excessive endurance training (overtraining) • Reduced performance, prolonged fatigue, etc. • Related to brain serotonin activity • Exercise begins and ends in the brain © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  8. Peripheral Fatigue: Neural Factors • Neuromuscular junction • Not a site for fatigue • Sarcolemma and transverse tubules • Ability of muscle membrane to conduct an action potential • Inability of Na+/K+ pump to maintain action potential amplitude and frequency • Can be improved by training • An action potential block in the T-tubules • Reduction in Ca+2 release from sarcoplasmic reticulum © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  9. Peripheral Fatigue: Mechanical Factors • Cross-bridge cycling and tension development depends on: • Arrangement of actin and myosin • Ca+2 binding to troponin • ATP availability • Fatigue may be due to: • H+ interference with Ca+2 binding to troponin • Inability of sarcoplasmic reticulum to take up Ca+2 • Lack of ATP • Inhibition of Ca+2 release from SR • Damage to actin and myosin © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  10. Peripheral Fatigue: Energetics of Contraction • Mismatch between rate of ATP production and utilization • Fatigue results in slowing of ATP utilization to preserve homeostasis • Accumulation of Pi • Muscle fiber recruitment in increasing intensities of exercise • Type I  Type IIb  Type IIx • Progression from most to least oxidative fiber type • Exercise >75% VO2max requires IIx fibers • Results in increased lactate production © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  11. Order of Muscle Fiber Type Recruitment Figure 19.3 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  12. Factors Limiting Ultra Short-Term Performances • Events lasting <10 seconds • Dependent on recruitment of Type II muscle fibers • Generate great forces that are needed • Motivation, skill, and arousal are important • Primary energy source • Anaerobic • Phosphocreatine © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  13. Factors Affecting Fatigue in Ultra Short-Term Events Figure 19.4 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  14. Factors Limiting Short-Term Performances • Events lasting 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 • Results in elevated lactate levels © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  15. Factors Affecting Fatigue in Short-Term Events Figure 19.5 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  16. Factors Limiting Moderate-Length Performances • Events lasting 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 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  17. Factors Affecting Fatigue in Aerobic Performances Lasting 3–20 Minutes Figure 19.6 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  18. Factors Limiting Intermediate-Length Performances • Events lasting 21–60 minutes • Predominantly aerobic • Usually conducted at less than 90% VO2max • Environmental factors are important • Heat • Humidity • State of hydration © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  19. Factors Affecting Fatigue in Aerobic Performances Lasting 21–60 Minutes Figure 19.7 © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  20. Factors Limiting Long-Term Performances • Events lasting 1–4 hours • Environmental factors important • Ability to deal with heat and humidity • Maintain rate of carbohydrate utilization • Muscle and liver glycogen • Diet and fluid ingestion influence performance © 2007 McGraw-Hill Higher Education. All Rights Reserved.

  21. Factors Affecting Fatigue in Aerobic Performances Lasting 1–4 Hours Figure 19.8 © 2007 McGraw-Hill Higher Education. All Rights Reserved.