What is RQ?

• A. Rate of oxygen consumption
• B. Ratio of CO2 production to nitrogen excretion
• C. Net energy expenditure per liter of oxygen
• D. Respiratory quotient, defined as the ratio of CO2 production to O2 consumption

Answer: (D)

RQ is the respiratory quotient, defined as the ratio of carbon dioxide production to oxygen consumption. It comes from measuring gas exchange during indirect calorimetry and tells you which fuels the body is oxidizing for energy. When carbohydrates are the main fuel, CO2 is produced in amounts that track closely with O2 use, giving an RQ near 1.0. Fat oxidation requires more oxygen per CO2 produced, yielding an RQ around 0.7. Protein oxidation tends to be about 0.8, though nitrogen excretion can affect the exact value. This concept is about gas exchange and substrate use, not the rate of oxygen consumption alone, nor a ratio involving nitrogen excretion, nor a measure of energy expenditure per liter of oxygen.