What is the expected respiratory quotient (RQ) during low-energy sustainable exercise?

During low-energy sustainable exercise, the expected respiratory quotient (RQ) typically drops to around 0.7. This value is associated with a metabolic state where the body primarily utilizes fat for energy rather than carbohydrates. The RQ is a measure of the ratio of carbon dioxide produced to oxygen consumed, and it reflects the predominant source of fuel being metabolized.

At an RQ of 0.7, fat oxidation is favored, a scenario that often occurs during prolonged, steady-state aerobic activities such as walking or light cycling. This kind of exercise is characterized by a lower intensity where the energy demands of the body can be met by the oxidative metabolism of fat.

In contrast, a higher RQ value, such as 1.0, suggests a reliance on carbohydrates as the primary energy source, which is more typical during intense or maximal exercise. Similarly, an RQ around 0.9 indicates a mixed use of fats and carbohydrates, commonly seen in moderate exercises. An RQ closer to 0.8 can occur but is less common during low-energy sustainable exercise compared to the clear pattern of fat oxidation represented by the value of 0.7. Thus, the RQ of 0.7 is the most representative of energy metabolism