If a performer is predominantly using carbohydrates for energy, the Respiratory Exchange Ratio (RER) is expected to be close to which value?

If a performer is predominantly using carbohydrates for energy, the Respiratory Exchange Ratio (RER) is expected to be close to which value?

• A. 0.7
• B. 0.85
• C. 1.0
• D. 1.25

Answer: (C)

RER shows how much CO2 is produced for every unit of O2 consumed, reflecting which fuels are driving energy production. When carbohydrates are the main fuel, glucose oxidation uses roughly equal amounts of O2 and produces CO2 in a 1:1 ratio, so the RER is about 1.0. Fat oxidation, by contrast, requires more O2 relative to CO2, giving around 0.7. A mixed fuel mix sits around 0.85, and values above 1.0 can occur briefly during very intense efforts due to buffering processes, but they aren’t typical for carbohydrate-dominant metabolism. So, with predominant carbohydrate use, the RER is close to 1.0.

RER shows how much CO2 is produced for every unit of O2 consumed, reflecting which fuels are driving energy production. When carbohydrates are the main fuel, glucose oxidation uses roughly equal amounts of O2 and produces CO2 in a 1:1 ratio, so the RER is about 1.0. Fat oxidation, by contrast, requires more O2 relative to CO2, giving around 0.7. A mixed fuel mix sits around 0.85, and values above 1.0 can occur briefly during very intense efforts due to buffering processes, but they aren’t typical for carbohydrate-dominant metabolism. So, with predominant carbohydrate use, the RER is close to 1.0.