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