Energy Systems Flashcards
Oxygen Kinematics, Estimating Energy
Can you name the mechanism behind direct calorimetry?
It is measured through heat - for example a heat-insulated chamber.
Can you name the mechanism behind indirect calorimetry?
This is measured through calculations of substrate used and expelled - for example, oxygen and carbon dioxide.
The rate of O2 and CO2 exchanged in the lungs normally equals the rate of their usage and release by the body tissues.
Why does VO2 sometimes have a dot above the V?
The dot above the V in V̇O₂ represents a rate or volume per unit of time. This notation is common in physiology and exercise science.
V̇O₂ (with the dot) refers to oxygen consumption rate, usually measured in liters per minute (L/min) or milliliters per kilogram per minute (mL/kg/min).
VO₂ (without the dot) simply refers to the volume of oxygen, without specifying the time component.
What is VO2, at its core, and what is its formula?
Hint: it involves dots!
V̇O₂ (oxygen consumption) is the volume of oxygen your body uses per minute.
V.O2 = (V.i x FiO2) - (V.e x FeO2)
Vi = volume of air inspired / minute
FiO2 = fraction of inspired oxygen (~20.95% of air is oxygen)
Ve= volume of air expired (breathed out) per minute
FeO2 = fraction of expired oxygen (this is lower than inspired because your body used some oxygen)
V̇O₂ is a measure of aerobic fitness (more V̇O₂ max = more endurance).
What is VCO2, at its core, and what is its formula?
Hint: it’s the same…
VCO2 (carbon dioxide production) is the volume of CO₂ your body produces per minute. Your body takes in a very small amount of CO₂ from the air (~0.03%) but exhales much more CO₂ because your cells produce it as waste.
V.CO2 = (V.e x FeCO2) - (V.i x FiCO2)
Ve= volume of air expired (breathed out) per minute
FeCO2 = fraction of expired CO2 (this is higher than inspired because your body produced more)
Vi = volume of air inspired per minute
FiO2 = fraction of inspired CO2 (~0.03% of air is oxygen)
V̇CO₂ hints at metabolic activity (e.g., fat vs. carb burning).
What is the RER, and how it is calculated?
Respiratory Exchange Ratio
The ratio V̇CO₂ / V̇O₂ is called the Respiratory Exchange Ratio (RER), which tells whether your body is burning more carbohydrates or fats for energy.
For example, RER 0.71 = 100% of energy is derived from fats. Or, RER 1.00 = 100% of energy is derived from carbohydrates.
RER values between 0.71 and 1.00 indicate a mix of fat and carbohydrate metabolism.
What is the Haldane transformation?
Hint: it’s not on a graph!
The Haldane Transformation is a mathematical adjustment used in indirect calorimetry to calculate inspired ventilation (V̇i) when only expired ventilation (V̇e) is measured- we typically only measure expired air as it is easier.
However, since nitrogen (N₂) is not metabolized by the body (it is metabolically inert) the nitrogen content in inspired air must equal that in expired air. This allows us to estimate Vi by using expired gas fractions.
~0.7904 (since air is ~79% nitrogen)
The volume of N2 inhaled is equal to the volume of N2 exhaled.
What is the Haldane effect?
The Haldane Effect describes how oxygen binding to hemoglobin (Hb) reduces its affinity for CO₂, helping with CO₂ transport and release.
In the lungs, where oxygen levels are high:
O₂ binds to hemoglobin → Hemoglobin releases CO₂ (facilitates exhalation).
In the tissues, where oxygen levels are low:
Less O₂ bound to hemoglobin → Hemoglobin picks up more CO₂ (helps CO₂ transport back to lungs).
Gas Concentrations in Air
- Oxygen accounts for 20.93% (0.2093)
- CO2 accounts for 0.03% (0.0003)
- Nitrogen accounts for 79.03% (0.7903)
What is the relationship between gas consumption and energy expenditure?
Your body uses oxygen (O₂) to generate energy through aerobic metabolism. This process happens in the mitochondria, where oxygen helps break down carbohydrates (glucose) and fats to produce ATP (energy).
Since we can’t directly measure ATP production in real-time, we use oxygen consumption (V̇O₂) as a way to estimate energy expenditure.
Researchers have determined that for every 1 liter (L) of oxygen consumed, your body produces about 4.69 to 5.05 kcal of energy—depending on whether you’re burning fat or carbohydrates.
So in the aerobic sense, why is the RER for fat lower than for oxygen?
Even though fat has more energy per gram, it requires a lot more oxygen to be broken down into ATP compared to carbohydrates.
When oxidating glucose (which has more oxygen, and less C-H bonds), less oxygen is needed. When oxidating fat (lots of C-H bonds, less oxygen), more oxygen is needed.
Even though fats yield more total energy per gram, they do so less efficiently per unit of oxygen consumed.
What is average O2 consumption?
On average, this is 0.3L of O2 / min.
