The approach most commonly used to measure metabolic rate is to measure the rate of O2 consumption. Although there are small errors inherent in this method, it is easy, and provides a good estimate of metabolic rate. Why is the rate of oxygen consumption an appropriate measure of metabolic rate?

Metabolic rate is the amount of energy used per unit time. The production of usable energy in the form of ATP depends largely on aerobic respiration.

Metabolic rate is the amount of energy used per unit time. The hydrolysis of ATP to ADP and Pi is an aerobic process.

Metabolic rate is the amount of energy released in anabolic processes, and anabolic processes are aerobic.