1. Chapter 19 Factors 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

2. Factors Affecting Performance
Figure 19.1

3. Sites of Fatigue Fatigue Central fatigue Peripheral 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

4. Possible Sites of Fatigue
Figure 19.2

5. 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

6. 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

7. 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

8. 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

9. Order of Muscle Fiber Type Recruitment
Figure 19.3

10. 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

11. Factors Affecting Fatigue in Ultra Short-Term Events
Figure 19.4

12. 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

13. Factors Affecting Fatigue in Short-Term Events
Figure 19.5

14. 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

15. Factors Affecting Fatigue in Aerobic Performances Lasting 3–20 Minutes
Figure 19.6

16. 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

17. Factors Affecting Fatigue in Aerobic Performances Lasting 21–60 Minutes
Figure 19.7

18. 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

19. Factors Affecting Fatigue in Aerobic Performances Lasting 1–4 Hours
Figure 19.8