Final answer:
The respiratory exchange ratio (RER) is a measure of the ratio of carbon dioxide produced to oxygen consumed during respiration. It is used to determine the fuel source being metabolized and provides information about energy usage under different conditions.
Step-by-step explanation:
The respiratory exchange ratio (RER) is a measure of the ratio of carbon dioxide produced to oxygen consumed during respiration. It is represented by the formula RER = Vc/Vo, where Vc is the volume of carbon dioxide produced and Vo is the volume of oxygen consumed. RER is used to determine which fuel source is being metabolized, and it can provide information about a person's energy usage under different conditions.