The minimal rate of energy expenditure per unit time by warm-blooded animals at rest. It is reported in energy units per unit time ranging from watt (Joule/second) to ml O2/min or Joule per hour per kg body mass J/(h.kg)). Proper measurement requires a strict set of criteria be met. These criteria include being in a physically and psychologically undisturbed state, in a thermally neutral environment, while in the post-absorptive state (i.e., not actively digesting food). In bradymetabolic animals, such as fish and reptiles, the equivalent term Standard metabolic rate (SMR) is used. It follows the same criteria as BMR, but requires the documentation of the temperature at which the metabolic rate was measured. This makes BMR a variant of standard metabolic rate measurement that excludes the temperature data, a practice that has led to problems in defining "standard" rates of metabolism for many mammals.
"BMR is measured under very restrictive circumstances when a person is awake, but at complete rest."
Basal Metabolic Rate is the minimum calorific requirement needed to sustain life in a resting individual, or the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans).
BMR can be responsible for burning up to 70% of the total calories expended as you will expend energy no matter what you're doing, even when sleeping. Thus your Basal Metabolic Rate is the number of calories you'd burn if you were to stay in bed all day.
Basal metabolic rate is usually by far the largest component of total caloric expenditure.
However, the Harris-Benedict equations are only approximate and variation in BMR (reflecting varying body composition), in physical activity levels, and in energy expended in thermogenesis make it difficult to estimate the dietary consumption any particular individual needs in order to maintain body weight. 2000 kilo-calories is often quoted but is no more than a guideline.
BMR decreases with age and with the loss of lean body mass.
Increasing muscle mass increases BMR. Aerobic fitness level, a product of cardiovascular exercise, while previously thought to have effect on basal or resting metabolic rate (RMR), has been shown in the 1990s not to correlate with BMR, when fat-free body mass was adjusted for. New research has however come to light which suggests aerobic exercise does increase resting energy consumption. Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect one's overall energy expenditure as well as one's BMR.
BMR is measured under very restrictive circumstances when a person is awake, but at complete rest.
An accurate BMR measurement requires that the person's sympathetic nervous system not be stimulated. A more common and closely related measurement, used under less strict conditions, is resting metabolic rate (RMR).
To see how many calories you burn performing certain activities see How to Count and Calculate Calories
The BMR Calculator will calculate your Basal Metabolic Rate (BMR) - the number of calories you would burn if you were to stay in bed all day.
Studies published in 1992 and 1997 indicate the level of aerobic fitness of an individual does not have any correlation with the level of resting metabolism. Both studies find that aerobic fitness levels do not improve the predictive power of fat free mass for resting metabolic rate. Some studies suggest a minimum of 20 to 25 minutes of cardiovascular training per day can temporarily increase the basal metabolic rate by around 10%, owing to an increase in the metabolism of the working muscles required for recovery as well as storage of glycogen and other fuel sources used by the body like ATP and Creatine.