What does the RER formula consist of?

The respiratory exchange ratio (RER) is calculated using the formula that represents the ratio of carbon dioxide produced to oxygen consumed during respiration. Therefore, the correct answer focuses on the relationship between these two gases, specifically CO2 output over O2 input. This ratio is significant in metabolism as it indicates the relative contribution of carbohydrates versus fats to energy production during activity. For instance, higher values of RER suggest a greater reliance on carbohydrates, whereas lower values indicate fat oxidation.

In contrast, the other choices do not accurately describe the relationship measured by the RER. The first option suggests a division that is inverted, which does not reflect the physiological measurement being assessed. The third option combines the two gases in an additive form, which does not provide a meaningful ratio relevant for metabolic assessment. Lastly, the fourth choice implies a subtraction, which again does not relate to the RER concept used in exercise physiology and energy metabolism analysis.