© 2007 McGraw-Hill Higher Education. All Rights Reserved. Presentation revised and updated by Brian B. Parr, Ph.D. University of South Carolina Aiken Chapter 19 Factors Affecting Performance EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Objectives 1.Identify factors affecting maximal performance. 2.Provide evidence for and against the central nervous system being a site of fatigue. 3.Identify potential neural factors in the periphery that may be linked to fatigue. 4.Explain the role of cross-bridge cycling in fatigue. 5.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.

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Objectives 6.Describe the factors limiting performance in all-out activities lasting less than ten seconds. 7.Describe the factors limiting performance in all-out activities lasting 10 to 180 seconds. 8.Discuss the subtle changes in the factors affecting optimal performance as the duration of maximal performance increase from three minutes to four hours.

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Factors Affecting Performance Figure 19.1

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Sites of Fatigue  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

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Possible Sites of Fatigue Figure 19.2

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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 P i  Muscle fiber recruitment in increasing intensities of exercise –Type I  Type IIb  Type IIx –Progression from most to least oxidative fiber type Exercise >75% VO 2max requires IIx fibers Results in increased lactate production

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Order of Muscle Fiber Type Recruitment Figure 19.3

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Factors Affecting Fatigue in Ultra Short- Term Events Figure 19.4

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Factors Affecting Fatigue in Short-Term Events Figure 19.5

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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 VO 2max –Type II fibers recruited –High levels of lactate  Factors that interfere with O 2 delivery are limiting –Altitude –Anemia

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Factors Affecting Fatigue in Aerobic Performances Lasting 3–20 Minutes Figure 19.6

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Factors Limiting Intermediate-Length Performances  Events lasting 21–60 minutes  Predominantly aerobic  Usually conducted at less than 90% VO 2max  Environmental factors are important –Heat –Humidity –State of hydration

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Factors Affecting Fatigue in Aerobic Performances Lasting 21–60 Minutes Figure 19.7

© 2007 McGraw-Hill Higher Education. All Rights Reserved. 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

© 2007 McGraw-Hill Higher Education. All Rights Reserved. Factors Affecting Fatigue in Aerobic Performances Lasting 1–4 Hours Figure 19.8