Basal Metabolic Rate

Use This Calculator To Calculate The Amount of Energy Expenditure While Resting at Room Temperature
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Basal Metabolic Rate

Basal Metabolic Rate

Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state.

Post-absorptive state

It’s a state when the digestive system is inactive, which requires about twelve hours of fasting in humans.

The release of energy in this state is sufficient only for the functioning of the vital organs, such as the heart, lungs, brain and the rest of the nervous system, liver, kidneys, sex organs, muscles and skin.

Decrease in BMR:

BMR decreases with age and with the loss of lean body mass.

Increase in BMR:

Increased cardiovascular exercise and muscle mass can increase BMR.

Other Conditions that effect BMR:

Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect one's overall energy expenditure, and can affect one's BMR as revealed by gas analysis.

BMR is measured under very restrictive circumstances when a person is awake, but at complete rest.

To measure accurate BMR:

An accurate BMR measurement requires that the person's sympathetic nervous system is not stimulated. A more common and closely related measurement, used under less strict conditions, is resting metabolic rate (RMR).

Measurement of BMR and RMR:

BMR and RMR are measured by gas analysis through either direct or indirect calorimetry.

Rough Estimation of BMR and RMR:

Rough estimation can be acquired through an equation using age, sex, height, and weight.

Studies of energy metabolism using both methods provide convincing evidence for the validity of the respiratory quotient (R.Q.), Respiratory Quotient:

Respiratory quotient measures the inherent composition and utilization of carbohydrates, fats and proteins as they are converted to energy substrate units that can be used by the body as energy.

The original equations from Harris and Benedict are:

English BMR Formula:

Women: BMR = 655 + ( 4.35 x weight in pounds ) + ( 4.7 x height in inches ) - ( 4.7 x age in years )
Men: BMR = 66 + ( 6.23 x weight in pounds ) + ( 12.7 x height in inches ) - ( 6.8 x age in year )

Metric BMR Formula:

Women BMR = 655 + ( 9.6 x weight in kilos ) + ( 1.8 x height in cm ) - ( 4.7 x age in years )
Men: BMR = 66 + ( 13.7 x weight in kilos ) + ( 5 x height in cm ) - ( 6.8 x age in years )

About 70% of a human's total energy expenditure is due to the basal life processes within the organs of the body. About 20% of one's energy expenditure comes from physical activity and another 10% from thermo genesis, or digestion of food.

All of these processes require an intake of oxygen along with coenzymes to provide energy for survival and expel carbon dioxide, which is explained by the Krebs cycle.

What enables the Krebs cycle to perform metabolic changes to fats, carbohydrates, and proteins is energy which can be defined as the ability or capacity to do work.


The breakdown of large molecules into smaller molecules associated with release of energy is catabolism. The breakdown of proteins into amino acids is an example of catabolism


The building up process is termed anabolism. The formation of proteins from amino acids is an anabolic process.

Exergonic reactions

Exergonic reactions are energy-releasing reactions and are generally catabolic.

Undergone reactions

Undergone reactions require energy and include anabolic reactions and the contraction of muscle. Metabolism is the total of all catabolic, exergonic, anabolic, undergone reactions.

Adenosine Triphosphate (ATP)

ATP is composed of adenine, a nitrogen containing base, ribose, a five carbon sugar (collectively called adenosine), and three phosphate groups. Adenosine Triphosphate (ATP) is the intermediate molecule that drives the exergonic transfer of energy to switch to endergonic anabolic reactions used in muscle contraction.

This is what causes muscles to work which can require a breakdown, and also to build in the rest period, which occurs during the strengthening phase associated with muscular contraction. ATP is a high energy molecule because it stores large amounts of energy in the chemical bonds of the two terminal phosphate groups. The breaking of these chemical bonds in the Krebs Cycle provides the energy needed for muscular contraction.

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