Resting Metabolic Rate (RMR) is the amount of energy expended daily by humans at rest. Rest is defined as existing in a neutrally temperate environment while in the post-absorptive state.
The release, and using, of energy in this state is sufficient only for the functioning of the vital organs, the heart, lungs, nervous system, kidneys, liver, intestine, sex organs, muscles, and skin.
The body's generation of heat is known as thermogenesis and it can be measured to determine the amount of energy expended. RMR generally decreases with age and with the decrease in lean body mass. Increasing muscle mass increases RMR.
THINGS THAT AFFECT YOUR METABOLIC RATE
MUSCLE: More muscle increases your RMR.
AGE: Your RMR decreases with age.
GENETICS: A decrease in your RMR can be due to genetics.
THE WEATHER: Living in a cold enviroment can increase your RMR. I know this sounds strange but you expend more energy while moving around in cold weather. It's a alot easier to move around in summer but more of an effort to "get going" in winter.
MEALS: Small regular meals will increase your RMR.
PREGNANCY: It can increase your RMR.
CRASH DIETING: It will decrease your RMR.
SUPPLEMENTS: Some supplements can raise your RMR.
According to this formula, the woman in the example above has a BMR of 1204 kcal per day. During the last 100 years, lifestyles have changed and Frankenfield et al. showed it to be about 5% more accurate.