Basal metabolic rate (BMR), and the closely related resting metabolic rate (RMR), is 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). The release of energy in this state is sufficient only for the functioning of the vital organs, the heart, lungs and kidneys and the rest of the nervous system, intestine, liver, lungs, sex organs, muscles and skin. 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 BMR, …show more content…
The early work of the scientists J. Arthur Harris and Francis G. Benedict showed that approximate values could be derived using body surface area (computed from height and weight), age, and sex, along with the oxygen and carbon dioxide measures taken from calorimetry. Studies also showed that by eliminating the sex differences that occur with the accumulation of adipose tissue by expressing metabolic rate per unit of "fat-free" or lean body weight, the values between sexes for basal metabolism are essentially the same. Exercise physiology textbooks have tables to show the conversion of height and body surface area as they relate to weight and basal metabolic …show more content…
2. production and regulation of feelings of rage and aggression
3. regulation of body temperature
4. regulation of food intake, through two centers: o The feeding center or hunger center is responsible for the sensations that cause us to seek food. When sufficient food or substrates have been received and leptin is high, then the satiety center is stimulated and sends impulses that inhibit the feeding center. When insufficient food is present in the stomach and ghrelin levels are high, receptors in the hypothalamus initiate the sense of hunger. o The thirst center operates similarly when certain cells in the hypothalamus are stimulated by the rising osmotic pressure of the extracellular fluid. If thirst is satisfied, osmotic pressure decreases.
All of these functions taken together form a survival mechanism that causes us to sustain the body processes that BMR and RMR measure.
BMR estimation formulas
Several prediction equations exist. Historically most notable was Harris-Benedict equation, which was created in 1919. The original equations from Harris and Benedict are:
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