Chapter 19 Factors Affecting Performance

1. Chapter 19 Factors Affecting Performance EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley

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 in fatigue

3. Objectives • 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 • Describe the factors limiting performance in all-out activities lasting less than 10 seconds • Describe the factors limiting performance in all-out activities last 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

4. Factors Affecting Performance Fig 19.1

5. Sites of Fatigue • Central fatigue • Peripheral fatigue • Neural factors • Mechanical factors • Energetics of contraction Fig 19.2

6. 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 • Excessive endurance training (overtraining) • Reduce performance capacity, prolonged fatigue, altered mood states, sleep disturbance, loss of appetite, and increased anxiety

7. 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

8. Peripheral FatigueMechanical 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

9. Peripheral FatigueEnergetics 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 IIb  Type IIx • Progression from most to least oxidative fiber type • Results in increased lactate production

10. Muscle Fiber Type Recruitment Fig 19.3

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

12. Ultra Short-Term Performance < 10 sec Fig 19.4

13. Short-Term Performance10-180 seconds • Shift from anaerobic to aerobic metabolism • 70% energy supplied anaerobically at 10s • 60% supplied aerobically at 180s • Primary energy source • Anaerobic glycolysis

14. Short-Term Performance10-180 seconds Fig 19.5

15. 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

16. Moderate-Length Performance3-20 minutes Fig 19.6

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

18. Intermediate-Length Performance 21-60 minutes Fig 19.7

19. Long-Term Performance1-4 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

20. Long-Term Performance1-4 hours Fig 19.8

21. Chapter 19 Factors Affecting Performance