Chapter 19: Factors Affecting Performance EXERCISE PHYSIOLOGY Theory and Application to Fitness and...
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Transcript of Chapter 19: Factors Affecting Performance EXERCISE PHYSIOLOGY Theory and Application to Fitness and...
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
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
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
Factors Affecting Performance
Fig 19.1
Sites of Fatigue
• Central fatigue• Peripheral fatigue
– Neural factors– Mechanical
factors– Energetics of
contraction
Fig 19.2
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
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
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
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
Muscle Fiber Type Recruitment
Fig 19.3
• < 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
Ultra Short-Term Performance
Ultra Short-Term Performance < 10 sec
Fig 19.4
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
Short-Term Performance 10-180 seconds
Fig 19.5
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
Moderate-Length Performance 3-20 minutes
Fig 19.6
Intermediate-Length Performance 21-60 minutes
Predominantly aerobic
• Usually conducted at less than 90% VO2max
• Environmental factors are important– Heat– Humidity– State of hydration
Intermediate-Length Performance 21-60 minutes
Fig 19.7
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
Long-Term Performance 1-4 hours
Fig 19.8