Respiratory Exchange Ratio
The respiratory exchange ratio (RER), also called the respiratory quotient (RQ), is the ratio of carbon dioxide produced to oxygen consumed during metabolism. Introduced by J. B. Weir (1949), RER is a non-invasive indirect measure of substrate utilization—indicating whether the body is primarily oxidizing carbohydrate, fat, or protein. RER values range from approximately 0.7 (pure fat oxidation) to 1.0 (pure carbohydrate oxidation) and higher under anaerobic conditions. By measuring exhaled and inhaled gases during exercise, RER reveals which fuel source predominates at different intensities, providing insights into metabolic flexibility and exercise physiology.
Source record
Citations copied verbatim from the method’s source record. No claim-level verification is inferred from them.
- Weir, J. B. (1949). New methods for calculating metabolic rate with special reference to protein metabolism. Journal of Physiology, 109(1-2), 1-9. · DOI 10.1113/jphysiol.1949.sp004363
- Frayn, K. N. (1983). Calculation of substrate oxidation rates in vivo from gaseous exchange. Journal of Applied Physiology, 55(2), 628-634. · DOI 10.1152/jappl.1983.55.2.628
- Jeukendrup, A. E., & Wallis, G. A. (2005). Measurement of substrate oxidation during exercise by means of gas exchange measurements. International Journal of Sports Medicine, 26(1), S28-S37. · DOI 10.1055/s-2004-830512
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