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 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 IIb  Type IIx Progression from most to least oxidative fiber type Results in increased lactate production

Muscle Fiber Type Recruitment Fig 19.3

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 < 10 sec Fig 19.4

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 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 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 1-4 hours Fig 19.8