Energy Expenditure & Oxygen

• What do metabolic processes result in?

  heat production
• Substrate metabolism efficiency:

  • 40% = ATP
  • 60% = heat
• Heat production rate defines what?

  metabolic rate
• heat production defines metabolic rate:

  • heat production increases with increased energy production
  • calorie (kcal) represents unit of heat measurement (caloric output)
  • calorimetry is the measurement of heat transfer (quantify heat production)
• The kilocalorie and food energy:

  • = unit of energy
  • = amount of energy needed to raise the temperature of 1 kg of water by 1°
  • measured with bomb calorimeter
• Quantifying human energy expenditure:

  All metabolic processes ultimately…

  • depend on oxygen use
  • result in heat production
• …depend on oxygen use:

  • humans are oxidative species
  • most energy satisfied by oxidative phosphorylation
  • results in heat production

  Indirect Calorimetry:

  • assesses human energy metabolism
  • via measuring O2 consumption and CO2 production
• …result in heat production

  Direct Calorimetry:

  • assesses human energy metabolism
  • via measuring heat production
• Direct Calorimetry:

  • human calorimeter = direct measure of heat production and kcal expended
  • measure how much the water is heating at a given time to determine kcal
  • change in heat allows us to determine how much kcal is being expended
• Indirect Calorimetry:

  • measuring rate of O2 uptake provides indirect but accurate estimate of energy expenditure

  2 types:

  • closed-circuit spirometry
  • open-circuit spirometry
• Closed-circuit spirometry:

  • rebreathing 100% O2 in a closed system
  • rate of volume reduction = VO2 in L/min
  • as individual breathes, number of molecules within tank will fall
  • you breathe in less O2 and breathe out less CO2
• Open-circuit Spirometry:

  • measure inspired and expired O2 volumes
  • magnitude of difference divided by time = VO2 in L/min
  • rate of O2 consumption
• Indirect Calorimetry:

  • oxidative metabolism of glucose and fat
  • uses O2 and produces CO2 and water
  • rate of O2 and CO2 exchange in lungs = rate of their usage and release by tissue
  • energy expenditure can be estimated by measuring these variables at the mouth
• Measurement:

  • O2 inspired > O2 expired
  • CO2 inspired < CO2 expired
  • VO2 = inspired - expired
  • VCO2 = expired - inspired
• Measuring energy expenditure:

  • to estimate amount of energy used, you must know what food substrate is being oxidized
  • amount of O2 used during metabolism depends on type of fuel being oxidized
  • use VO2 and VCO2 from indirect calorimetry to determine substrate utilization and quantify energy expenditure
• amount of O2 needed to oxidize 1 molecule of CHO or FAT is proportional to amount of carbon in fuel:

  • C6H12O6 + 6 O2 —> 6 CO2 + 32 ATP + 6 H2O
  • C16H32O2 + 23 O2 —> 16 CO2 + 106 ATP + 16 H2O
• Respiratory Exchange Rate (RER):

  • ratio of CO2 production and O2 uptake
  • RER = VCO2 / VO2
  • RER for 1 molecule of glucose = 1.00
  • RER for 1 molecule of palmitic acid (fat) = 0.70
  • predicts substrate use, kcals, O2 efficiency
• RER, substrate utilization, energy yield:

  • RER gives idea of substrate utilization and energy yield
  • different contributions of carbohydrates and fat at different RER ratios
  • higher RER = carbohydrates
  • lower RER = fat
  • carbohydrates = less kcal dense; requires less O2; less efficient storage of energy
  • fat = more kcal dense; requires more O2; more efficient storage of energy
• Respiratory Quotient (RQ):

  • RQ and RER are same measurement but obtained differently
  • RQ = cell respiration
  • RER = exhaled air from lungs
  • RQ range = 0.70 — 1.00
  • RER range = <0.70 — >1.20
• RER ≠ RQ:

  • hyperventilation = increase CO2 output
  • metabolic acidosis = more lactate in blood + more H ions (H + bicarbonate = CO2)
  • non-steady-state exercise = transition to different intensity (VCO2 takes longer to reach steady state than VO2)
  • prolonged exercise = amino acid oxidation
• Review:

  • different activities require different levels of energy
  • metabolic rate = rate at which the body uses energy/rate at which ATP must be resynthesized
  • metabolic rate = whole-body VO2
  • therefore VO2 = metabolic rate
• Energy expenditure at rest:

  • = resting basal metabolic rate
  • BMR = minimal amount of energy needed to carry out physiological functions
  • energy intake - energy output = energy balance
• Energy expenditure during exercise:

  • increase power output = increase motor units = increase energy demand = increase energy supply
• What does metabolism help us do?

  resupply ATP
• What is VO2max?

  it is our maximal O2 uptake
• Physiological definition of VO2max:

  • the highest rate at which the body can take up, transport, and utilize O2 to perform muscle work
• Measuring VO2max

  • increase muscle work = increase VO2
  • amount of O2 being consumed reflects O2 demand
  • muscle work rate = O2 demand
  • VO2 = O2 supply rate
• 2 protocols:

  • ramp
  • step
  • both cause an increase in O2 demand under different circumstances
• Exercise protocols to identify VO2:

  • both ramp and step protocols cause an increase in O2 demand which causes an increase in O2 supply
  • eventually demand becomes too great that we cannot supply it anymore
  • this is our VO2max
• Maximal Oxygen Uptake (VO2max):

  • what is the primary criteria for determination?

  VO2 fails to increase despite a rise in speed or work rate; plateau
• O2 demand > O2 supply rate
• Secondary criteria for determination:

  1. HR (220-age)
  2. RER > 1.15 (ratio between fat and carbs, O2 and CO2)
  3. RCP (hyperventilation)
  4. blood lactate concentration (>8mM; lactate produces CO2)
  5. RPE (19-20/20)
  6. validation/verification tests
• VO2max and constant work rate:

  • capitalizes on known characteristics of VO2 response that occur for all intensities above critical power
  • highest intensity where we can achieve submaximal steady VO2
  • above critical power, the length of time we can maintain exercise decreases
• How do we test that VO2max is actually our VO2max?

  perform a validation trial

  • first = ramp
  • second = step
• Discrepancies:

  • RER is not a perfect measure
  • verification measure is not always accurate
• How to express VO2max:

  VO2max (L/min) —> absolute

  • (measure)…
  • female = 2.00
  • male = 3.50
  • difference = 43%
  • range = 2.0 — 4.5

  VO2max (mL/min/kg) —> relative

  • (compare)…
  • female = 40.0
  • male = 50.0
  • difference = 20%
  • range = 15 — 60
• VO2max and modality:

  • activities requiring more muscle mass will result in more O2
  • modality changes VO2max results (due to amount and type of muscles)
• VO2max and fitness status:

  • fitness status based on genetics and training
  • with training, body changes in ways that allow body to better take up O2 and transport it through the body
  • fitter individuals = higher O2 demand and greater VO2max
• Importance of VO2max:

  • a predictor of endurance and exercise performance
  • a sensitive measure of training effectiveness
  • a predictor of mortality in clinical populations
• What does it mean when VO2 levels are not in a steady state?

  it means we are drawing upon anaerobic energy sources