Bioenergetics of Exercise And Training

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Bioenergetics of Exercise And Training
chapter 2
Bioenergeticsof Exercise and Training
Joel T. Cramer, PhD CSCS,D NSCA-CPT,D FNSCA
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Key Terms

• bioenergetics The flow of energy in a biological
  system the conversion of macronutrients into
  biologically usable forms of energy.
• catabolism The breakdown of large molecules into
  smaller molecules, associated with the release of
  energy.
• anabolism The synthesis of larger molecules from
  smaller molecules can be accomplished using the
  energy released from catabolic reactions.
• (continued)

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Key Terms (continued)

• exergonic reactions Energy-releasing reactions
  that are generally catabolic.
• endergonic reactions Require energy and include
  anabolic processes and the contraction of muscle.
  
• metabolism The total of all the catabolic or
  exergonic and anabolic or endergonic reactions in
  a biological system.
• adenosine triphosphate (ATP) Allows the transfer
  of energy from exergonic to endergonic reactions.

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Figure 2.1
Chemical structureof an ATP Molecule
(a) The chemical structure of an ATP molecule
including adenosine (adenine ribose),
triphosphate group, and locations of the
high-energy chemical bonds. (b) The hydrolysis of
ATP breaks the terminal phosphate bond, releases
energy, and leaves ADP, an inorganic phosphate
(Pi), and a hydrogen ion (H). (c) The hydrolysis
of ADP breaks the terminal phosphate bond,
releases energy, and leaves AMP, Pi, and H.
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Biological Energy Systems

• Three basic energy systems exist in muscle cells
  to replenish ATP
• The phosphagen system
• Glycolysis
• The oxidative system

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Key Point

• Energy stored in the chemical bonds of adenosine
  triphosphate (ATP) is used to power muscular
  activity. The replenish-ment of ATP in human
  skeletal muscle is accomplished by three basic
  energy systems (1) phosphagen, (2)
  glycolytic,and (3) oxidative.

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Biological Energy Systems

• Phosphagen System
• Provides ATP primarily for short-term,
  high-intensity activities (e.g., resistance
  training and sprinting) and is active at the
  start of all exercise regardless of intensity

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Biological Energy Systems

• Phosphagen System
• ATP Stores
• The body does not store enough ATP for exercise.
• Some ATP is needed for basic cellular function.
• The phosphagen system uses the creatine kinase
  reaction to maintain the concentration of ATP.
• The phosphagen system replenishes ATP rapidly.
• Control of the Phosphagen System
• Law of mass action The concentrations of
  reactants or products (or both) in solution will
  drive the direction of the reactions.

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Biological Energy Systems

• Glycolysis
• The breakdown of carbohydrateseither glycogen
  stored in the muscle or glucose delivered in the
  bloodto resynthesize ATP

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Figure 2.2
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Biological Energy Systems

• Glycolysis
• The end result of glycolysis (pyruvate) may
  proceed in one of two directions
• 1) Pyruvate can be converted to lactate.
• ATP resynthesis occurs at a faster rate but is
  limited in duration.
• This process is sometimes called anaerobic
  glycolysis (or fast glycolysis).
• (continued)

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Biological Energy Systems

• Glycolysis
• The end result of glycolysis (pyruvate) may
  proceed in one of two directions (continued)
• 2) Pyruvate can be shuttled into the
  mitochondria.
• When pyruvate is shuttled into the mitochondria
  to undergo the Krebs cycle, the ATP resynthesis
  rate is slower, but it can occur for a longer
  duration if the exercise intensity is low enough.
• This process is often referred to as aerobic
  glycolysis (or slow glycolysis).

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Biological Energy Systems

• Glycolysis
• Glycolysis and the Formation of Lactate
• The end result is not lactic acid.
• Lactate is not the cause of fatigue.
• Cori Cycle
• Lactate can be transported in the blood to the
  liver, where it is converted to glucose.
• This process is referred to as the Cori cycle.

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Figure 2.3
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Biological Energy Systems

• Glycolysis
• Glycolysis Leading to the Krebs Cycle
• Pyruvate that enters the mitochondria is
  converted to acetyl-CoA.
• Acetyl-CoA can then enter the Krebs cycle.
• The NADH molecules enter the electron transport
  system, where they can also be used to
  resynthesize ATP.

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Biological Energy Systems

• Glycolysis
• Energy Yield of Glycolysis
• Glycolysis from one molecule of blood glucose
  yields a net of two ATP molecules.
• Glycolysis from muscle glycogen yields a net of
  three ATP molecules.

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Key Term

• lactate threshold (LT) The exercise intensity or
  relative intensity at which blood lactate begins
  an abrupt increase above the baseline
  concentration.

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Figure 2.4
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Biological Energy Systems

• Glycolysis
• Lactate Threshold and Onset of Blood Lactate
• LT begins at 50 to 60 of maximal oxygen
  uptakein untrained individuals.
• It begins at 70 to 80 in trained athletes.
• OBLA is a second increase in the rate of lactate
  accumulation.
• It occurs at higher relative intensities of
  exercise.
• It occurs when the concentration of blood lactate
  reaches 4 mmol/L.

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Biological Energy Systems

• The Oxidative (Aerobic) System
• Primary source of ATP at rest and during
  low-intensity activities
• Uses primarily carbohydrates and fats as
  substrates

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Biological Energy Systems

• The Oxidative (Aerobic) System
• Glucose and Glycogen Oxidation
• Metabolism of blood glucose and muscle glycogen
  begins with glycolysis and leads to the Krebs
  cycle. (Recall If oxygen is present in
  sufficient quantities, the end product of
  glycolysis, pyruvate, is not converted to lactate
  but is transported to the mitochondria, where it
  is taken up and enters the Krebs cycle.)
• ATP is produced from ADP.

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Figure 2.5
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Table 2.1
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Biological Energy Systems

• The Oxidative (Aerobic) System
• Fat Oxidation
• Triglycerides stored in fat cells can be broken
  down by hormone-sensitive lipase. This releases
  free fatty acids from the fat cells into the
  blood, where they can circulate and enter muscle
  fibers.
• Some free fatty acids come from intramuscular
  sources.
• Free fatty acids enter the mitochondria, are
  broken down, and form acetyl-CoA and hydrogen
  protons.
• The acetyl-CoA enters the Krebs cycle.
• The hydrogen atoms are carried by NADH and FADH2
  to the electron transport chain.

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Table 2.2
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Biological Energy Systems

• The Oxidative (Aerobic) System
• Protein Oxidation
• Protein is not a significant source of energy for
  most activities.
• Protein is broken down into amino acids, and the
  amino acids are converted into glucose, pyruvate,
  or various Krebs cycle inter-mediates to produce
  ATP.
• Control of the Oxidative (Aerobic) System
• Isocitrate dehydrogenase is stimulated by ADP and
  inhibited by ATP.
• The rate of the Krebs cycle is reduced if NAD
  and FAD2 are not available in sufficient
  quantities to accept hydrogen.
• The ETC is stimulated by ADP and inhibited by
  ATP.

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Figure 2.7
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Biological Energy Systems

• Energy Production and Capacity
• In general, there is an inverse relationship
  between a given energy systems maximum rate of
  ATP production (i.e., ATP produced per unit of
  time) and the total amount of ATP it is capable
  of producing over a long period.
• As a result, the phosphagen energy system
  primarily supplies ATP for high-intensity
  activities of short duration, the glycolytic
  system for moderate- to high-intensity activities
  of short to medium duration, and the oxidative
  system for low-intensity activities of long
  duration.

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Table 2.3
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Table 2.4
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Key Point

• The extent to which each of the three energy
  systems contributes to ATP production depends
  primarily on the intensity of muscular activity
  and secondarily on the duration. At no time,
  during either exercise or rest, does any single
  energy system provide the complete supply of
  energy.

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Substrate Depletion and Repletion

• Phosphagens
• Creatine phosphate can decrease markedly
  (50-70) during the first stage (5-30 seconds)
  of high-intensity exercise and can be almost
  eliminated as a result of very intense exercise
  to exhaustion.
• Postexercise phosphagen repletion can occur in a
  relatively short period complete resynthesis of
  ATP appears to occur within 3 to 5 minutes, and
  complete creatine phosphate resynthesis can occur
  within 8 minutes.

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Substrate Depletion and Repletion

• Glycogen
• The rate of glycogen depletion is related to
  exercise intensity.
• At relative intensities of exercise above 60 of
  maximal oxygen uptake, muscle glycogen becomes an
  increasingly important energy substrate the
  entire glycogen content of some muscle cells can
  become depleted during exercise.

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Substrate Depletion and Repletion

• Glycogen
• Repletion of muscle glycogen during recovery is
  related to postexercise carbohydrate ingestion.
• Repletion appears to be optimal if 0.7 to 3.0 g
  of carbohydrate per kg of body weight is ingested
  every 2 hours following exercise.

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Table 2.5
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Low-Intensity, Steady-StateExercise Metabolism

• Figure 2.8 (next slide)
• 75 of maximal oxygen uptake (VO2max)
• EPOC excess postexercise oxygen consumption
• VO2 oxygen uptake

.
.
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Figure 2.8
Low-Intensity, Steady-StateExercise Metabolism

• 75 of maximal oxygen uptake (VO2max)
• EPOC excess postexercise oxygen consumption
• VO2 oxygen uptake

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Key Term

• excess postexercise oxygen consumption (EPOC)
  Oxygen uptake above resting values used to
  restore the body to the preexercise condition
  also called postexercise oxygen uptake, oxygen
  debt, or recovery O2.

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Metabolic Specificity of Training

• The use of appropriate exercise intensities and
  rest intervals allows for the selection of
  specific energy systems during training and
  results in more efficient and productive regimens
  for specific athletic events with various
  metabolic demands.

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Metabolic Specificity of Training

• Interval Training
• Interval training is a method that emphasizes
  bioenergetic adaptations for a more efficient
  energy transfer within the metabolic pathways by
  using predetermined intervals of exercise and
  rest periods.
• Much more training can be accomplished at higher
  intensities
• Difficult to establish definitive guidelines for
  choosing specific work-to-rest ratios

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Table 2.7
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Metabolic Specificity of Training

• Combination Training
• Combination training adds aerobic endurance
  training to the training of anaerobic athletes in
  order to enhance recovery (because recovery
  relies primarily on aerobic mechanisms).
• May reduce anaerobic performance capabilities,
  particularly high-strength, high-power
  performance
• Can reduce the gain in muscle girth, maximum
  strength, and speed- and power-related
  performance
• May be counterproductive in most strength and
  power sports