*Geek Box: Basal Metabolic Rate vs. Resting Metabolic Rate
You may often see basal metabolic rate [BMR] and resting metabolic rate [RMR] used, and it would be tempting to assume that these are interchangeable. However, while BMR and RMR seem similar, they do differ in some important ways.
BMR is measured in strict conditions, after a 12 h overnight fast, with no caffeine or physical activity in the 12 h prior to the measurement. Importantly, it is also conducted under “thermo-neutral” conditions, i.e., room temperature is held constant [~25°C/77°F]; this is to prevent the potential for colder temperatures to upregulate the body’s creation of heat [i.e., thermogenesis].
RMR generally has similar experimental conditions to BMR, for example, it is measured while participants are in a supine, but not sleeping, position. However, it is not necessarily measured under thermo-neutral conditions, and may also be measured in both the fasted state [which would be closest to BMR], but also in the postprandial state while participants are resting, to then calculate additional parameters such as the thermic effect of feeding.
Thus, when it comes to BMR and RMR, it is a case of “same-same, but different”. In the fasted state, both are considered the minimum amount of energy required to maintain basic body functions. However, BMR would be a more controlled measure, and thus ‘truer’ measure of this component of energy expenditure.