Copyright © 2006 Lippincott Williams & Wilkins. Human Energy Transfer During Exercise Chapter 6

Copyright © 2006 Lippincott Williams & Wilkins. Objectives Identify the body’s three energy systems, and explain their relative importance to exercise intensity and duration Describe differences in blood lactate threshold between sedentary and trained individuals Outline the time course for oxygen uptake during 10 minutes of moderate exercise

Copyright © 2006 Lippincott Williams & Wilkins. Objectives (cont’d) Draw a figure showing the relationship between oxygen uptake and exercise intensity during progressively increasing increments of exercise to maximum Differentiate between the body’s two types of muscle fibers

Copyright © 2006 Lippincott Williams & Wilkins. Objectives (cont’d) Explain differences in the pattern of recovery oxygen uptake from moderate and exhaustive exercise, and include factors that account for EPOC from each exercise mode Outline optimal recovery procedures from steady-rate and non–steady-rate exercise

Copyright © 2006 Lippincott Williams & Wilkins. Energy Systems Immediate energy –ATP-PCr Short-term energy –Lactic acid system Long-term energy –Aerobic system

Copyright © 2006 Lippincott Williams & Wilkins. ATP-PCr System Performances of ultra-short duration (< 6 seconds) and high intensity require an immediate and rapid supply of energy –100-m sprint –25-m swim –Smashing a tennis ball during the serve –Thrusting a heavy weight upwards

Copyright © 2006 Lippincott Williams & Wilkins. ATP-PCr System (cont’d) High-energy phosphates — phosphagens –Stored within skeletal muscle Adenosine triphosphate (ATP) Phosphocreatine (PCr) CP + ADP C + ATP

Copyright © 2006 Lippincott Williams & Wilkins. Lactic Acid System During intense exercise, intramuscular stored glycogen provides energy to phosphorylate ADP during glycogenolysis, forming lactate

Copyright © 2006 Lippincott Williams & Wilkins. Lactic Acid System (cont’d) Performances of short duration and high intensity that require rapid energy transfer that exceeds that supplied by phosphagens –400-m sprint –100-m swim –Multi-sprint sports

Copyright © 2006 Lippincott Williams & Wilkins. Lactic Acid System (cont’d) The lactate threshold (LT) –The exercise intensity prior to the abrupt increase in blood lactate –A.k.a onset of blood lactate accumulation (OBLA)

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Did You Know? World class athletes can sustain exercise intensities at 85 to 90% of their maximum capacity for aerobic metabolism before blood lactate accumulates

Copyright © 2006 Lippincott Williams & Wilkins. Lactate Shuttling It has been shown that lactate produced through glycogenolysis in one cell may be shuttled to another cell to provide fuel for further oxidation Thus, skeletal muscle is not only a major site of lactate production but is also a primary tissue for lactate removal via oxidation

Copyright © 2006 Lippincott Williams & Wilkins. Aerobic Energy System Aerobic metabolism provides the greatest proportion of energy transfer, particularly when exercise duration extends beyond 2 to 3 minutes

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Aerobic Energy System (cont’d) Oxygen deficit –Quantitatively represents the difference between the total oxygen actually consumed during exercise and the amount that would have been consumed had a steady-rate, aerobic metabolism occurred immediately at the initiation of exercise

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Aerobic Energy System (cont’d) Maximal oxygen consumption ( ) –The highest oxygen uptake achieved despite increases in exercise intensity –Represents an individual’s capacity for aerobically resynthesizing ATP

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Muscle Fiber Types Two distinct muscle fiber types exist in humans –Fast-twitch (FT) or type II muscle fibers –Slow-twitch (ST) or type I muscle fiber

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Muscle Fiber Types (cont’d) Type I muscle fibers are highly oxidative and are designed for prolonged endurance activities Type IIb muscle fibers are highly glycolytic and are designed for explosive activities

Copyright © 2006 Lippincott Williams & Wilkins. Muscle Fiber Types (cont’d) Type IIa muscle fibers are both oxidative and glycolytic and are designed for activities that are both aerobic and anaerobic in nature

Copyright © 2006 Lippincott Williams & Wilkins. Key Point The body’s energy systems should be viewed along a continuum of exercise bioenergetics

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Oxygen Uptake During Recovery: “Oxygen Debt” Oxygen consumption following exercise remains elevated for several minutes to several hours depending on the intensity and duration of exercise This elevation in oxygen consumption is often referred to as the “Oxygen Debt” or Excess Postexercise Oxygen Consumption (EPOC)

Copyright © 2006 Lippincott Williams & Wilkins. Oxygen Uptake During Recovery: “Oxygen Debt” (cont’d) Traditional view –Oxygen debt theory Alactacid oxygen debt Lactacid oxygen debt Modern view – EPOC theory

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Optimal Recovery Active aerobic exercise in recovery accelerates lactate removal Moderate aerobic exercise during recovery is clearly better for facilitating lactate removal compared to passive recovery

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