Post on 04-Jan-2016
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Factors Affecting Performance
Powers, Chapter 19
Factors Affecting Performance
Sites of Fatigue
• Central fatigue• Peripheral fatigue– Neural factors– Mechanical factors– Energetics of
contraction
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
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 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
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 IIa Type IIb– Progression from most to least oxidative fiber
type• Results in increased lactate production
Pattern of Muscle Fiber Recruitment
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
Ultra Short-Term Performance
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
Short-Term Performance
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
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
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
Long-Term Performance