When the Respiratory Exchange Ratio (RER) is greater than 1, it signifies that the body is significantly engaged in anaerobic respiration. This means that more carbon dioxide (CO2) is being produced than oxygen (O2) is being consumed.
The Respiratory Exchange Ratio (RER), also known as the Respiratory Quotient (RQ) when measured at the cellular level, is a key indicator of the type of fuel the body is utilizing and the metabolic processes occurring. It's calculated as the ratio of the volume of CO2 produced (VCO2) to the volume of O2 consumed (VO2):
RER = VCO2 / VO2
Understanding RER > 1
When the RER value surpasses 1.0, it indicates a specific physiological state:
- Anaerobic Respiration: This is the primary metabolic process indicated when RER is greater than 1.0. During intense physical activity, the body's oxygen supply may not be sufficient to meet the high energy demands through aerobic metabolism alone. To compensate, the body relies on anaerobic pathways.
- Excess CO2 Production: During anaerobic metabolism, particularly the buffering of lactic acid produced during high-intensity exercise, additional carbon dioxide is generated. This non-metabolic CO2 adds to the CO2 produced from fuel oxidation, leading to a disproportionately high VCO2 compared to VO2. This elevation in CO2 output artificially inflates the RER value above 1.0.
When Does RER Exceed 1?
The most common and significant scenario where RER is observed to be greater than 1.0 is during intense exercise.
- Maximal Effort Activities: Activities like sprinting, high-intensity interval training (HIIT), or lifting very heavy weights push the body into an oxygen deficit. The demand for ATP (energy) far exceeds the available oxygen, forcing the body to rely on anaerobic energy systems.
- Lactic Acid Buffering: As anaerobic glycolysis produces lactic acid, the body's bicarbonate buffering system works to neutralize it. This process generates additional CO2 that is then expelled through respiration, contributing to the RER rising above 1.0.
RER Values at a Glance
To provide context, here's a brief overview of typical RER values and their implications:
| RER Value (Approx.) | Primary Indication | Explanation |
|---|---|---|
| 0.7 | Predominantly Fat Metabolism | At rest or during very low-intensity exercise, the body primarily burns fats for energy. |
| 0.8 | Mixed Diet / Rest | This value is commonly associated with an individual consuming a mixed diet at rest, indicating a balance between fat and carbohydrate utilization. |
| 1.0 | Predominantly Carbohydrate Metabolism | During moderate-to-high intensity aerobic exercise, the body increasingly relies on carbohydrates (glucose) as the primary fuel source. At this point, the CO2 produced matches the O2 consumed for carbohydrate oxidation. |
| > 1.0 | Anaerobic Respiration / Intense Exercise | Indicates significant anaerobic activity where more CO2 is produced than O2 consumed. This is often due to the buffering of lactic acid produced during maximal effort, leading to an "excess" CO2 release independent of metabolic oxidation. |
In summary, an RER greater than 1.0 is a clear physiological signal that the body is operating under extreme metabolic stress, relying heavily on anaerobic pathways to meet energy demands, and generating additional CO2 through acid buffering processes.
