Measuring Energy Use in Humans

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Questions and Answers

Which form of biological work is primarily involved in muscle contraction?

  • Electrical
  • Chemical
  • Transport
  • Mechanical (correct)

What is the primary energy currency of the cell?

  • ATP (correct)
  • ADP
  • Glucose
  • Glycogen

What happens to ATP levels in skeletal muscle during extreme exercise conditions?

  • They significantly increase
  • They remain unchanged
  • They decrease (correct)
  • They stabilize

Which energy system primarily uses glucose as a substrate?

<p>Anaerobic Glycolysis (C)</p> Signup and view all the answers

Under normal resting conditions, how much ATP does the body store?

<p>80 to 100 g (D)</p> Signup and view all the answers

Which component of the Metabolic Cart differentiates it from the Douglas Bag Technique?

<p>Pneumotachometer (D)</p> Signup and view all the answers

What impact does an increase in body mass have on energy expenditure during weight-bearing exercises?

<p>Raises the energy expended (D)</p> Signup and view all the answers

What is the relationship between anaerobic contribution and oxygen debt during exercise?

<p>Oxygen debt arises as a result of anaerobic effort (B)</p> Signup and view all the answers

How can energy cost be expressed to allow for a fair comparison between individuals?

<p>As energy cost per kilogram of body mass (B)</p> Signup and view all the answers

Which factor is likely to decrease the influence of body mass on energy cost when engaging in weight-supported exercise?

<p>Lower resistance encountered (A)</p> Signup and view all the answers

What is the primary purpose of indirect calorimetry in measuring energy use?

<p>To calculate energy expenditure based on oxygen consumption (D)</p> Signup and view all the answers

Which component of Total Daily Energy Expenditure (TDEE) accounts for the highest percentage?

<p>Resting metabolic rate (A)</p> Signup and view all the answers

Which method used to measure energy expenditure is the most expensive?

<p>Doubly labeled water (D)</p> Signup and view all the answers

In measuring respiratory gas exchange, what does the Douglas Bag technique primarily measure?

<p>Fraction of expired O2 and CO2 (C)</p> Signup and view all the answers

How is energy expenditure calculated using the doubly labeled water method?

<p>Calculating differences in elimination rates of isotopes in excreted fluids (D)</p> Signup and view all the answers

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Study Notes

Measuring Energy Use in Humans

  • Total Daily Energy Expenditure (TDEE) is comprised of three main components:
    • Physical Activity (15-30%)
    • Dietary Induced Thermogenesis (~10%)
    • Resting Metabolic Rate (~60-75%)
  • Lean muscle mass plays a crucial role in TDEE

Methods Used to Measure Energy Use In Humans

  • Indirect Calorimetry: Measures respiratory gas exchange (Oxygen consumed and carbon dioxide produced)
    • Open circuit and closed-circuit spirometry two types of indirect calorimetry
    • Douglas Bag Technique: Collects expired air, measures volume and fraction of oxygen and carbon dioxide, then calculates VO2 and VE.
    • Metabolic Cart: Modernized version of the Douglas Bag Technique using a pneumotachometer, mixing chamber, continuous sampling, and automation.
  • Doubly Labeled Water: Isotope-based method used for free-living individuals.
    • Participants consume water containing labeled H2 and O2, collects all their excreted urine & saliva, then calculates the difference between elimination rates to determine energy use and excretion.

Energy Use During Different Activities

  • Rowing, running, and cycling (2 km) have high energy costs

  • Swimming (2 miles/hour) and running (5 miles/hour) have different energy costs; factors like body mass, stroke rate, and water resistance are considerations.

  • Influence of Body Mass: Larger body mass increases energy expenditure, especially in weight-bearing exercise.

    • Weight-supported exercise (stationary cycling) has a reduced influence of body mass.

Biological Work in Humans

  • Three forms of biological work (energy consuming processes):
    • Chemical: Biosynthesis
    • Mechanical: Muscle contraction
    • Transport: Transfer of substances between cells

1st Law of Thermodynamics

  • Energy can be transformed from one form to another but cannot be created or destroyed.

ATP (Adenosine Triphosphate): The Cell’s Energy Currency

  • Composed of adenosine linked to three phosphates.
  • ATPase catalyzes the reaction of ATP with water to form ADP (Adenosine Diphosphate).

ATP: A Limited Currency

  • Cells only store a small amount of ATP and must continually resynthesize it.
  • ATP levels decrease significantly in skeletal muscle only under extreme exercise conditions.
  • The body stores 80-100 g of ATP under normal resting conditions, enough for 2-3 seconds of maximal exercise.

Energy Systems: Metabolic Pathways to Regenerate ATP

  • Four main energy systems regenerate ATP:
    • Phosphagen System (ATP-CP)
    • Anaerobic Glycolysis (glucose/CHO)
    • Aerobic System (CHO)
    • Lipid (fat)

The Body’s Energy Sources

  • Carbohydrate stores:
    • Muscle glycogen ~300 g
    • Liver glycogen ~100 g
    • Blood glucose ~ 10 g (essential for CNS)
  • Lipid stores:
    • Total store ~10,000 g (average 67 kg person at 15% body fat)
      • Significantly more energy per gram of lipid than CHO.

Respiratory Exchange Ratio (RER)

  • Estimate of the Respiratory Quotient (RQ) which is the ratio of CO2 produced to O2 consumed.
  • Indicates which fuel is predominantly being used during exercise.
  • RER values:
    • Fat ~ 0.7
    • Carbohydrate ~ 1.0
    • Assumes negligible protein use.

Fat Dynamics During Exercise

  • Light-to-moderate-intensity exercise:
    • Fatty acids provide the predominant energy source in light intensity exercise.
    • Energy derives from equal amounts of carbohydrate and fat in moderate intensity exercise.

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