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

Factors Affecting Performance Figure 19.1

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

Possible Sites of Fatigue Figure 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 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

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

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

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

Order of Muscle Fiber Type Recruitment Figure 19.3

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

Factors Affecting Fatigue in Ultra Short-Term Events Figure 19.4

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

Factors Affecting Fatigue in Short-Term Events Figure 19.5

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

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

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

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

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

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