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The respiratory exchange rate (RER) is a physiological value calculated in a lab via metabolic cart. It allows us to estimate exercise intensity, the fuel resources for a specific exercise or physical activity, and in some cases, suspect having possible health problems.
In theory, RER ranges from zero (0) to and endless number, yet in actuality, it ranges from about 0.7 L/L at rest all the way up to 1.45 L/L during maximal exercise (especially maximal aerobic exercise). The respiratory exchange rate isn calculated as dividing a person's CO2 production (VCO2) by their oxygen consumption (VO2).
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The scientific basis for the RER, is the fact that carbs, fats, and proteins have a carbon skeleton as molecules and while catabolized (broken down) as energy/fuel sources for different activities, they require a certain ratio of oxygen to carbon atoms to be catabolized. As the ratio of oxygen required to the number of carbon atoms in the molecule's skeleton changes between carbs, fat, and protein, so does the RER that results mathematically.
Thus, breaking down carbs is commonly represented by a certain RER range of values, while breaking down fats is commonly represented by a different certain RER range of values, and breaking down proteins is commonly represented by its own certain RER range of values. Thus, the RER value becomes indicative of the main molecule used to produce most of the energy under the specific circumstances that result in a certain RER value.
A person's RER is commonly around the 0.7 mark. the fact that the value is a mathematical fraction, means that their VO2 is greater than their VCO2, indicative of using fat as the main fuel for energy production under these specific circumstances. Since there are 8 billion people on Earth, RER at rest is not exactly 0.7 for all, yet is pretty close.
RER values between 0.7 and 1.00 (excluding one unique outlier to be explain later on) is indicative of fats being the dominant fuel for energy production. An RER of 1.0 exactly bears the meaning of an even split (50:50) between energy production from carbs and fats. This means the 50% of the energy is produced from carbs, and the other 50% if produced from fats (assuming proteolysis is completely insignificant).
Any RER value above 1.01 is indicative of creating energy dominantly by breaking down carbs as the fuel for the activity or exercise. The more the RER value climbs above 1.01, the greater the percentage of energy produced by breaking carbs. Another distinction that RER allows us to make is how the energy is dominantly produced in terms of aerobic energy (with oxygen) vs anaerobic energy (without oxygen).
RER values of 0.7 - 0.99 are indicative of energy being produced dominantly aerobically, while RER values of 1.01 and above are indicative of energy being produced dominantly anaerobically. An RER value of 1.00 is indicative of a 50:50 split between how much energy is produced aerobically, and how much is produced anaerobically.
An extremely unique RER value is a constant value of 0.8. If a person's RER remains 0.8 for a prolonged time, and does not increase nor decrease with the increase or decrease in workload or intensity, this could be indicative of abnormal metabolism where as proteins are the dominant fuel source for the activity. Usually, the body aspires to produce 3% of the energy from proteins, and NO MORE.
Thus, if most of the energy is being produced from proteins, something is wrong, and perhaps, awfully wrong. There is a good chance that the RER is 0.8 since your body is undergoing abnormally extensive breakdown of proteins and skeletal muscle mass. This is known as a pathology called Rhabdomyolysis. Rhabdo as in "rapido" which means fast or extensive; "myo" is the prefix for anything muscle related; and "lysis" means breaking down or the death of.
Thus, Rhabdomyolysis is the medical outcome of abnormal metabolism, resulting in the abnormally high catabolism of skeletal muscles. Rhbdomyolysis (often abbreviated as Rhabdo). Rhabdomyolysis increases dramatically the physiological challenge on the liver, causing possible liver dysfunction at different extents.
The longer and more the Rhabdomyolysis continues, the worse the liver damage. Rhabdomyolysis can lead to death within four hours of beginning. In addition to a constant RER of 0.8 (non-responsive to changes in workload and intensity), brown urine is a hallmark sign of Rhabdomyolysis. The two together leave little room, if at all, for a misdiagnosis of Rhabdomyolysis.
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Since RER is based on knowing VCO2 and VO2, a metabolic cart capable of gas analysis on a breath by breath basis is required. For this reason, it is likely that you would need the services of a lab with metabolic services that include such gas analysis.
Last, an RER of 1.1 or greater is used as one of four possible criteria to determine if a person has reached their maximal VO2 or not. An RER value of 1.1 or above is indicative of possibly reaching your maximal VO2, yet not everyone's RER is going to be 1.1 as they reach their maximal VO2.
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