What provides the most personalized assessment of an individual's true metabolic function?

The resting metabolic rate (RMR) test provides the most personalized assessment of an individual's true metabolic function because it measures the number of calories the body burns at rest to maintain basic physiological functions. This test captures the metabolic rate in a controlled environment, typically done after fasting and in a rested state, which offers a precise estimate of basal metabolism.

In contrast, other options like field metabolic tests and submaximal fitness tests tend to estimate energy expenditure based on general formulas and activity levels, making them less individualized than the RMR test. The cardiopulmonary exercise test is valuable for assessing aerobic fitness and cardiovascular efficiency but does not solely focus on metabolic rate. Therefore, the RMR test stands out as the most direct and individualized measure of metabolic function.