Understand the definitions of Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR). BMR is the amount of energy expended by the body to maintain basic physiological functions (e.g., breathing, circulation, and cellular processes) under strict conditions, such as complete rest, fasting, and a thermoneutral environment. RMR, on the other hand, is similar but measured under less strict conditions, such as after light activity or without a strict fasting requirement.