Chapter 4 Exercise Metabolism and Bioenergetics

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Chapter 4Exercise Metabolism and Bioenergetics
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Objectives

• After this presentation, the participant will be
  able to
• Describe the primary methods of how the body
  produces energy for exercise.
• Differentiate between and define aerobic and
  anaerobic metabolism.
• Distinguish which energy pathways are used for
  various intensities and durations of exercise.
• Understand the interaction of carbohydrate, fat,
  and protein as fuels for exercise.
• State the differences in the energy use during
  steady state and exhaustive exercise.
• Describe basic training-induced adaptations in
  energy production.

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Bioenergetics

• Bioenergetics is the study of how energy is
  transformed through various biochemical reactions
• Metabolism refers to all the chemical reactions
  that occur in the body to maintain itself
• Exercise metabolism refers to the examination of
  bioenergetics as it relates to the unique
  physiologic changes and demands placed on the
  body during exercise

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Nutrient Substrates

• Proteins, carbohydrates, and lipids (fats)
  constitute the main substrates used to transfer
  metabolic energy to be used for all types of
  cellular activity and life
• Carbohydrates provide the body with a source of
  fuel and energy required for all daily activities
  including exercise.
• The storage form of carbohydrates, called
  glycogen

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Nutrient Substrates

• Another important source of energy is fat. The
  chemical or substrate form in which most fat
  exists in food as well as in the body is called
  triglycerides. Fat is mainly used as fuel during
  low intensity, long duration exercise.
• The third fuel source is protein. But protein
  rarely supplies much energy during exercise.
  During a low calorie diet, protein can be used as
  fuel to supply carbohydrates via gluconeogenesis.
  This is why muscle loss typically happens when
  using the low calorie method of dieting.
• Gluconeogenesis The formation of glucose from
  noncarbohydrate sources, such as amino acids.

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Energy and Work

• Adenosine Triphosphate is one of the primary
  sources of immediate energy for cellular
  metabolism stored in chemical bonds
• When the chemical bonds that hold ATP together
  are broken, energy is released and utilized for
  cellular work. This leaves behind another
  molecule called adenosine diphosphate (ADP)
• To perform mechanical work ATP is required

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Energy and Work

• ATP-PC system- Provides energy for short duration
  high intensity work, by replenishing ATP rapidly
  (6-10 seconds)
• Glycolysis- Provides energy through the breakdown
  of glucose to create ATP for moderate intensity,
  moderate duration work (30-50 seconds)
• Oxidative system-The most complex of the three
  energy systems is the process that uses
  substrates with the aid of oxygen to generate
  ATP.

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The Oxidative System

• The three oxidative or aerobic systems include
• 1. Aerobic glycolysis
• 2. The Krebs cycle
• 3. The electron transport chain (ETC)
• Fat can also be metabolized aerobically. Fat is
  the preferred fuel source for aerobic activities
  of long duration like a marathon.
• The first step in the oxidation of fat is a
  process referred to as ß-oxidation
• Produces lots of ATP, but very slowly

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Energy During Exercise

• Intensity and duration of exercise are inversely
  related.
• The amount of energy available from stored ATP
  and phosphocreatine is small, whereas the amount
  of energy from stored carbohydrate has a greater
  capacity, but is still limited
• The amount of available fuel for exercise from
  fats is essentially unlimited.

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Energy During Exercise

• Costs of exercise vary depending on conditions
• Lying supine burns fewer calories than standing
  exercise
• The body prefers oxidative metabolism
• Excess postexercise oxygen consumption- Elevated
  oxygen consumption after strenuous exercise
• During intermittent work glycolysis provides
  energy for work, oxidative provides recovery

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Fuel Contribution During Exercise

• The bioenergetics of exercise can be indirectly
  measured in a laboratory using various modes of
  exercise by measuring the respiratory quotient.
• The respiratory quotient (RQ) is the amount of
  carbon dioxide (CO2) expired divided by the
  amount of oxygen (O2) consumed, measured during
  rest or at steady state of exercise using a
  metabolic analyzer
• An RQ of 1.0 indicates that carbohydrate is
  supplying 100 of the fuel
• An RQ of 0.7 indicates that fat is supplying
  100 of the fuel.
• An RQ between 0.7 and 1.0 indicates a mixture.

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Summary

• Bioenergetics is the study of how energy is
  transformed through various biochemical reactions
• Metabolism refers to all the chemical reactions
  that occur in the body to maintain itself
• Proteins, carbohydrates, and lipids (fats)
  constitute the main substrates used
• ATP is the chemical form of energy derived from
  three pathways
• RQ determines percentage of fat, carbs, or
  protein utilized in exercise