Tuesday, 28 May 2024

Respiratory Exchange Ratio (RER)

The Respiratory Exchange Ratio (RER) is a measure that determines the ratio between the volume of CO2 produced by the body and the amount of O2 consumed. This calculation allows us to estimate the contribution of fats and carbohydrates to energy production and determine total energy expenditure.

RER versus RQ

The ratio of O2 to CO2 exchange at the cellular level is referred to as the respiratory quotient (RQ). However, measuring RQ directly is challenging, so we use an indirect measurement called the respiratory exchange ratio (RER). The RER provides an estimation of the RQ and is often used interchangeably with the term RQ.

How to Calculate RER

Calculating RER involves dividing the volume of CO2 produced by the volume of O2 consumed. This is done through a process called indirect calorimetry, which uses a spirometer (or another device to measure airflow or breath volume), as well as oxygen and carbon dioxide analyzers.

RER = Volume of CO2 removed from the body / Volume of O2 consumed
RER = VCO2 / VO2

Understanding the Numbers

RER values typically range from 0.7 to 1.0. A low RER value (0.7) indicates the body is primarily burning fat for fuel, while a high RER value (1.0) suggests carbohydrate burning. Values between the two show a mix of fuels being utilized.

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These values depend on the substrate being metabolized, which is influenced by an individual’s diet. Most individuals consuming a mixed diet of carbohydrates, protein, and fats will have a resting RER value of approximately 0.82. An RQ of 1.0 indicates 100% carbohydrate oxidation, which occurs during high exercise intensities. A value of 0.7 indicates 100% fatty acid oxidation and is typically observed during fasting. The oxidation of dietary protein does not have a specific RQ value due to the complexity of how different amino acids are metabolized.

Other factors that may impact the respiratory quotient include energy balance, changes in body mass, circulating insulin levels, and insulin sensitivity.

RER During Exercise

During rest, the RER value typically falls between 0.7 and 1.0, depending on the body’s fuel utilization. However, during exercise, the RER can exceed 1.0. This elevated RER can be used to measure the anaerobic threshold and indicate when an individual reaches their VO2max. Several factors, including a plateau in oxygen uptake, reaching maximal heart rate, achieving a respiratory exchange ratio of 1.15 or higher, and experiencing volitional exhaustion, help determine if an athlete has reached their peak VO2.


  • Q: How is RER calculated?

    • A: RER is calculated by dividing the volume of CO2 removed from the body by the volume of O2 consumed.
  • Q: What do RER values indicate?

    • A: RER values reflect the ratio of fats to carbohydrates being utilized for energy production. A low RER suggests fat burning, while a high RER indicates carbohydrate burning.
  • Q: What factors can affect the respiratory quotient?

    • A: Energy balance, changes in body mass, circulating insulin levels, and insulin sensitivity can all impact the respiratory quotient.
  • Q: How can RER be used during exercise?

    • A: During exercise, an elevated RER value indicates the anaerobic threshold and helps determine if an individual has reached their maximum oxygen uptake (VO2max).
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Understanding the Respiratory Exchange Ratio (RER) is valuable for assessing the contribution of fats and carbohydrates to energy production. By calculating RER, we can gain insights into an individual’s metabolic processes and make informed decisions regarding exercise intensity and fuel utilization.

For more information about RER and other related topics, visit Auralpressure.