Basal metabolic rate
[1] In bradymetabolic animals, such as fish and reptiles, the equivalent term standard metabolic rate (SMR) applies.
[2] Basal metabolic rate is the amount of energy per unit of time that a person needs to keep the body functioning at rest.
Some of those processes are breathing, blood circulation, controlling body temperature, cell growth, brain and nerve function, and contraction of muscles.
In humans, BMR typically declines by 1–2% per decade after age 20, mostly due to loss of fat-free mass,[3] although the variability between individuals is high.
[5] Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect one's overall energy expenditure as well as one's BMR.
[6] BMR may be measured by gas analysis through either direct or indirect calorimetry, though a rough estimation can be acquired through an equation using age, sex, height, and weight.
BMR is a flexible trait (it can be reversibly adjusted within individuals), with, for example, lower temperatures generally resulting in higher basal metabolic rates for both birds[7] and rodents.
This latter measurement has been criticized by Eric Liknes, Sarah Scott, and David Swanson, who say that mass-specific metabolic rates are inconsistent seasonally.
[15][16] A study by the American Society of Clinical Nutrition found that an experimental group of female volunteers had an 11.5% average increase in 24 hour energy expenditure in the two weeks following ovulation, with a range of 8% to 16%.
This group was measured via simultaneously direct and indirect calorimetry and had standardized daily meals and sedentary schedule in order to prevent the increase from being manipulated by change in food intake or activity level.
[18] The early work of the scientists J. Arthur Harris and Francis G. Benedict showed that approximate values for BMR 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.
Exercise physiology textbooks have tables to show the conversion of height and body surface area as they relate to weight and basal metabolic values.
For example, a 55-year-old woman weighing 130 pounds (59 kg) and 66 inches (168 cm) tall would have a BMR of 1,272 kilocalories (5,320 kJ) per day.
[26] A cross-sectional study of more than 1400 subjects in Europe and the US showed that once adjusted for differences in body composition (lean and fat mass) and age, BMR has fallen over the past 35 years.
[27] About 70% of a human's total energy expenditure is due to the basal life processes taking place in the organs of the body (see table).
[30] 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.
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 composed of adenine, a nitrogen containing base, ribose, a five carbon sugar (collectively called adenosine), and three phosphate groups.
The fatty acid molecule is broken down and categorized based on the number of carbon atoms in its molecular structure.
The structural components of the body that contain these amino acids are continually undergoing a process of breakdown and replacement.
for albumin is 0.818: The reason this is important in the process of understanding protein metabolism is that the body can blend the three macronutrients and based on the mitochondrial density, a preferred ratio can be established which determines how much fuel is utilized in which packets for work accomplished by the muscles.
Protein catabolism (breakdown) has been estimated to supply 10% to 15% of the total energy requirement during a two-hour aerobic training session.
The oxidative system (aerobic) is the primary source of ATP supplied to the body at rest and during low intensity activities and uses primarily carbohydrates and fats as substrates.
Both studies find that aerobic fitness levels do not improve the predictive power of fat free mass for resting metabolic rate.
Muscle contributes to the fat-free mass of an individual and therefore effective results from anaerobic exercise will increase BMR.
[39] This theory has been bolstered by several new studies linking lower basal metabolic rate to increased life expectancy, across the animal kingdom—including humans.
Calorie restriction and reduced thyroid hormone levels, both of which decrease the metabolic rate, have been associated with higher longevity in animals.
However, the ratio of total daily energy expenditure to resting metabolic rate can vary between 1.6 and 8.0 between species of mammals.
A decrease in food intake will typically lower the metabolic rate as the body tries to conserve energy.
