Factors Affecting Performance Factors Affecting Performance Sites of

Factors Affecting Performance

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 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 10 s – 60% supplied aerobically at 180 s • 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 VO 2 max – Type II fibers recruited – High levels of lactate • Factors that interfere with O 2 delivery are limiting – Altitude, anemia

Moderate-Length Performance

Intermediate-Length Performance • • 21 -60 minutes Predominantly aerobic Usually conducted at less than 90% VO 2 max 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