APK3110-Ch4-ExMetab_Spring+2012 (1)

APK3110-Ch4-ExMetab_Spring+2012 (1) - EXERCISE METABOLISM...

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EXERCISE METABOLISM Chapter 4
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Objectives 1. Define oxygen deficit and debt, EPOC and lactate threshold 2. Discuss explanations for rise in blood lactate concentration during incremental exercise 3. List the factors that regulate fuel selection during different types of exercise 4. Explain why fat metabolism is dependent on carbohydrate metabolism
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Resting Energy Expenditure At rest, ATP is produced almost 100% aerobically Oxygen consumption (VO 2 ) provides an index of aerobic ATP production (aerobic metabolism) During rest: 70kg person = 0.25 L/min VO 2 3.5 ml/kg/min Because oxygen is readily available at rest, pyruvate enters the Krebs cycle rather than being converted to lactate…so, blood lactate levels are low ( <1 mmol/L ) Acetyl-CoA Krebs Cycle
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Rest Exercise Transition At the onset of exercise: ATP demand increases instantaneously VO 2 does NOT increase instantaneously Figure 4.1 For light to moderate exercise, steady-state VO 2 occurs within 1-4 min Overlap of systems: 1. ATP-PC 2. Glycolysis
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Exercise Onset Figure 4.2 Oxygen Deficit - Lag in VO 2 at the onset of exercise Provides information about the regulation of oxidative phosphorylation Trained subjects have a lower oxygen deficit Better-developed aerobic bioenergetic capacity due to cardiovascular or muscular adaptations to exercise training Aerobic metabolism is active earlier → Less lactic acid produced
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Why does oxidative phosphorylation not achieve full activation instantaneously at exercise onset? Two hypotheses: 1. Inadequate oxygen supply to muscles at exercise onset Mitochondria may not have oxygen molecules present and therefore available to participate in the ETC…thus restricting aerobic ATP production This may hold true at very high intensity work 2. Delay in stimuli (ADP and Pi concentrations) to fully activate oxidative phosphorylation “Inertia of metabolism”
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Recovery from Exercise Oxygen Debt – elevated VO 2 (above resting levels) following exercise “Rapid” Phase (2-3 min) ~20% of oxygen debt Resynthesis of PC Replenishing muscle and blood oxygen stores “Slow” Phase (>30 min) ~80% of oxygen debt Conversion of lactic acid to glucose in the liver (gluconeogenesis) Figure 4.3 Phrase coined by A.V. Hill “Repayment” of oxygen deficit
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Oxygen Debt or EPOC? We now know that only about 20% of the “oxygen debt” is used for post- exercise liver gluconeogenesis EPOC – excess post- exercise oxygen consumption Often used interchangeably with “oxygen debt”
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Oxygen Deficit and EPOC are Intensity-Dependent Figure 4.3 With higher intensity exercise: Higher body temperature Greater depletion of PC Greater blood concentrations of lactic acid Higher levels of blood epinephrine and norepinephrine
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APK3110-Ch4-ExMetab_Spring+2012 (1) - EXERCISE METABOLISM...

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