Chapter 19 Factors Affecting Performance

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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
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Factors Affecting Performance
Figure 19.1
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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

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Possible Sites of Fatigue
Figure 19.2
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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

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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 Ca2 release from sarcoplasmic
  reticulum

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Peripheral Fatigue Mechanical Factors

• Cross-bridge cycling and tension development
  depends on
• Arrangement of actin and myosin
• Ca2 binding to troponin
• ATP availability
• Fatigue may be due to
• H interference with Ca2 binding to troponin
• Inability of sarcoplasmic reticulum to take up
  Ca2
• Lack of ATP
• Inhibition of Ca2 release from SR
• Damage to actin and myosin

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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 gt75 VO2max requires IIx fibers
• Results in increased lactate production

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Order of Muscle Fiber Type Recruitment
Figure 19.3
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Factors Limiting Ultra Short-Term Performances

• Events lasting lt10 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

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Factors Affecting Fatigue in Ultra Short-Term
Events
Figure 19.4
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Factors Limiting Short-Term Performances

• Events lasting 10180 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

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Factors Affecting Fatigue in Short-Term Events
Figure 19.5
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Factors Limiting Moderate-Length Performances

• Events lasting 320 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

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Factors Affecting Fatigue in Aerobic Performances
Lasting 320 Minutes
Figure 19.6
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Factors Limiting Intermediate-Length Performances

• Events lasting 2160 minutes
• Predominantly aerobic
• Usually conducted at less than 90 VO2max
• Environmental factors are important
• Heat
• Humidity
• State of hydration

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Factors Affecting Fatigue in Aerobic Performances
Lasting 2160 Minutes
Figure 19.7
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Factors Limiting Long-Term Performances

• Events lasting 14 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

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Factors Affecting Fatigue in Aerobic Performances
Lasting 14 Hours
Figure 19.8