1. Chapter 19: Factors Affecting Performance
EXERCISE PHYSIOLOGY
Theory and Application to Fitness and Performance, 5th edition
Scott K. Powers & Edward T. Howley
Presentation revised and updated by
TK Koesterer, Ph.D., ATC
Humboldt State University

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 ten 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 3 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, & 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 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

9. 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 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 of recruitment of Type II muscle fibers
Generate 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 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

14. Short-Term Performance 10-180 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 Performance 3-20 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 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

20. Long-Term Performance 1-4 hours
Fig 19.8