Biological Sciences
Metabolic Rate
Metabolic rate refers to the rate at which an organism expends energy through various metabolic processes, such as respiration, digestion, and circulation. It is a measure of the overall energy expenditure of an organism and is influenced by factors such as age, sex, body size, and activity level. Metabolic rate is often used as an indicator of an organism's physiological state and health.
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7 Key excerpts on "Metabolic Rate"
eBook - PDF- A. J. Marshall(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
XIX. ENERGY METABOLISM 221 III. Standard Metabolic Rate and Body Weight A. STANDARD Metabolic Rate The term standard Metabolic Rate (Krogh, 1916) refers to the heat production per unit of time as measured under conditions selected to provide a valid basis for making comparisons among individuals and species. Standard metabolism is also commonly called basal meta-bolism, but because of the clinical implications of this term we prefer to avoid it in the present discussion. The basic objective in the selection of standard experimental conditions is to minimize extrinsic influences on the metabolism of the organism so that the only major variable involved is the inherent metabolic intensity. Because of the lability of metabolic processes this objective can be attained only by the most rigorous techniques and attention to detail. For homoiotherms, the attainment of standard conditions requires that the animal be in a postabsorptive condition (i.e. not digesting or absorbing food), that it be in thermoneutral surroundings, and that it be as completely as possible at muscular and psychical rest. Benedict (1938) notes additional factors, such as ovulation, time of day (see Section V), molting (see Section VI), which influence the heat production and which accordingly must be recognized and controlled in comparative investigations. In addition, it is evident that the ambient temperature to which the animals are adapted (see Section IV, D.) may affect the standard Metabolic Rate if it is more than 15-20° below the standard (thermoneutral) temperature of the determination. Data on the standard Metabolic Rate of sixty species of birds are assembled in Table II. Only those data which were obtained under standard or quasi-standard conditions have been included, with a few exceptions as noted in the table. It should be clearly understood that the averages presented for the various species are not of uniform statistical reliability.
eBook - PDFPhysiological Ecology
How Animals Process Energy, Nutrients, and Toxins
- William H. Karasov, Carlos Martínez del Rio(Authors)
- 2020(Publication Date)
- Princeton University Press(Publisher)
1.3.1 Gillooly’s Equation and the Metabolic Theory of Ecology Equation 1.12 is very important because it summarizes the combined effect of body size and temperature on Metabolic Rate. We call it “Gillooly’s equation” to recognize James Gillooly’s insight about the multiplicative effect of allometry and temperature on metabolism. Gillooly’s equation summarizes a fundamental property of organisms. It tells us that the rate at which energy flows through an organism depends on how big and how hot the organism is. Recall from box 1.2 that we can estimate the fractional rate of energy input into the energy pool of an organism as the ratio of the energy flux and the energy pool contained in the organism, which is proportional to body mass. Thus, the fractional rate of metabolism (or “mass-specific metabolism”, b = B / m b ) can be expressed as (1.15) b m e b E kT i ∝ ( ) . – / – / 1 4 B A S I C C O N C E P T S 33 Figure 1.11. When all measurements are standard-ized to 20 º C, differences in Metabolic Rate are reduced. The regression lines are the same lines shown in figure 1.5 and derived by Hem-mingsen (1960). Birds and mammals have tempera-ture-corrected Metabolic Rates that are higher than those of reptiles and amphibians, but the overlap in values between the two groups is extensive. The dif-ference between unicellular organisms and ectothermic poikilotherms is very small. A significant fraction— albeit not all—of the variation in mass-corrected Metabolic Rate is explained by variation in body tem-perature. homeotherms at 39° C poikilotherms at 20° C unicells at 20° C Body mass (kg) Metabolic Rate (W) 10 -15 10 -9 10 -3 10 3 10 9 10 -15 10 -10 10 -5 1 10 5 Again, recall from box 1.2 that the residence time is the reciprocal of a fractional rate. Thus, the residence, or turnover, time of metabolic substrates ( t b ) should be proportional to the reciprocal of equation 1.15: (1.16) These equations summarize relationships that have been studied for a very long time.
eBook - PDFKinanthropometry and Exercise Physiology Laboratory Manual: Tests, Procedures and Data
Volume One: Anthropometry and Volume Two: Exercise Physiology
- Roger Eston, Thomas Reilly, Roger Eston, Thomas Reilly(Authors)
- 2020(Publication Date)
- Routledge(Publisher)
PART THREE ASSESSMENT OF ENERGY AND EFFICIENCY 6 Metabolic Rate AND ENERGY BALANCE Carlton B.Cooke 6.1 AIMS The aims in this chapter are to: – describe methods of measuring Metabolic Rate and energy balance, – describe methods of predicting resting Metabolic Rate, – describe methods of measuring energy expenditure using expired air analysis, – provide examples of the measurement of Metabolic Rate and energy balance. 6.2 BASAL Metabolic Rate (BMR) The main component of daily energy expenditure in the average person is the energy expenditure for maintenance processes, usually called basal Metabolic Rate (BMR). The BMR is the energy expended for the ongoing processes in the body in the resting state, when no food is digested and no energy is needed for temperature regulation. The BMR reflects the body’s heat production and can be determined indirectly by measuring oxygen uptake under strict laboratory conditions. No food is eaten for at least 12 hours prior to the measurement so there will be no increase in the energy required for the digestion and absorption of foods in the digestive system. This fast ensures that measurement of BMR occurs with the subject in the postabsorptive state. In addition, no undue muscular exertion should have occurred for at least 12 hours prior to the measurement of BMR. Normally, a good time to make a measurement of BMR is after waking from a night’s sleep, and in a hospital situation BMR is typically measured at this time. In laboratory practicals and exercise physiology experiments involving volunteer subjects, it is often impossible to obtain the correct conditions for a true measure of BMR. It is likely that in a laboratory practical the subject will have eaten a meal in the preceding 12 hours, which will increase metabolism in certain tissues and organs such as the liver. This is known as the specific dynamic effect.
eBook - PDF- Marie Dunford, J. Doyle, Marie Dunford(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
54 Chapter 02 Defining and Measuring Energy much smaller contributors. There are times when it is beneficial to calculate the individual components of TEE, particularly RMR and energy expended from physical activities. However, much of the time, it may be best to measure TEE or the amount of energy ex- pended in a 24-hour period so that it can be compared to 24-hour food intake. Basal and resting metabolism. The major compo- nent of TEE is basal metabolism. Basal metabolism re- fers to the energy necessary to keep the body alive at complete rest. Many life-sustaining body processes re- quire energy (that is, ATP). Breathing is an obvious one, but energy is also needed to circulate blood throughout the body, move food through the digestive system, ab- sorb nutrients, conduct nerve signals, maintain body temperature, and so on. In other words, basal metabo- lism is the minimal energy expenditure compatible with life. It is typically measured in the morning soon after waking after an overnight fast, with the person lying su- pine at complete rest in a temperature-controlled room. When determined under these conditions in the labora- tory, the measurement is referred to as basal Metabolic Rate (BMR). Most people are studied in a state of wakefulness at different times throughout the day, which requires slightly more energy than the basal level (for example, food must be digested, and body temperature must be maintained in a room where the temperature is not precisely controlled). This is referred to as resting me- tabolism and its measurement is the resting Metabolic Rate (RMR) discussed previously. Although BMR and RMR are often used interchangeably, there is a slight difference between them in measurement methodol- ogy and the energy required. Resting metabolism is about 10 percent greater than basal metabolism. Nu- trition and exercise professionals should take care to use the terms BMR and RMR correctly.
eBook - PDF- Kalyan Annamalai, Ishwar K. Puri, Milind A. Jog(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
If it is assumed that each unit mass of BS contains the same number of cells, then the specific metabolic energy release (J/kg) over life span is a good measure of cell Metabolic Rate. Consider a BS of body mass m, volume V, and surface area A. The rate of heat loss is pro-portional to the difference in temperature between the body surface and the temperature of the surroundings (T 0 ). Assuming the surface temperature is the same as T, the minimum specific Metabolic Rate (q ˙ M ) required to overcome heat loss is given as: q ˙ M (kW/kg) = Q ˙ /m b = h H A(T – T 0 )/m b . (14.102) Where h H is the heat transfer coefficient in kW/m 2 K and Q ˙ is heat loss rate in kW. If the body surface area of BS, A ∝ R 2 Char where R char is the characteristic size of BS and mass of BS, m b ∝ R Char 3 , then A ∝ m b 2/3 (empirical relation A ∝ m b 0.664 ): A/m b ∝ 1/R Char ∝ 1/m 1/3 , (14.103) q ˙ M ∝ 1/m b 1/3 → q ˙ M = C M m b –1/3 , (14.104) where C M is constant. The empirical fit of experimental data indicates: q ˙ M (W/kg) = C M m b –0.26 , (14.105) where C m = 3.552 (W/kg 0.74 ) and q ˙ m is given in (W/kg). While simple theory predicts the expo-nent to be –0.333, empirical experimental fit yields the exponent to be –0.26. If ATP production is accounted for, the energy release rate must be more than the value given by Equation 14.102 since the energy release rate must be equal to a sum of heat loss rate and energy for ATP produc-tion rate assuming ATP energy is not dissipated as heat. Assuming an average constant specific Metabolic Rate, and integrating Equation 14.105 over lifetime (t life ): q M,life (kJ/kg) = C M t life m b –1/3 . (14.106) Assuming a life span of 75 years, constant Metabolic Rate, and a 65 kg individual, q life = 2840 MJ/kg. This value seems reasonable when one compares it with literature values of 590–3025 MJ/kg. This is clearly an overestimate since specific Metabolic Rate keeps decreasing with increase in the mass.
- Carol J. Boushey, Ann M. Coulston, Cheryl L. Rock, Elaine Monsen(Authors)
- 2001(Publication Date)
- Academic Press(Publisher)
16 ].The Metabolic Rate of adult females fluctuates with the menstrual cycle. An average of 359 kcal/day difference in the BMR has been measured between its low point, about 1 week before ovulation at day 14, and its high point, just before the onset of menstruation. The mean increase in energy expenditure is about 150 kcal/day during the second half of the menstrual cycle [17 ]. During pregnancy, RMR decreases in the early stages, whereas later in pregnancy, the Metabolic Rate is increased by the processes of uterine, placental, and fetal growth and by the mother’s increased cardiac work [18 ].g. Environmental Influences.
REE is affected by extremes in environmental temperature. People living in tropical climates usually have RMRs that are 5–20% higher than those living in a temperate area. Exercise in temperatures greater than 86°F also imposes a small additional metabolic load of about 5% owing to increased sweat gland activity. The extent to which energy metabolism increases in extremely cold environments depends on the insulation available from body fat and protective clothing.2. MEASURING RESTING ENERGY EXPENDITURE: INDIRECT CALORIMETRY
The technique of indirect calorimetry has become the method of choice in most circumstances when a measurement of REE is needed. The term indirect refers to the fact that energy (heat) production is determined by measuring O2 consumption and CO2 production rather than directly measuring heat transfer. The equipment varies but a ventilated hood system is most commonly used. A clear plastic hood is placed over the subject’s head and made airtight around the neck (Fig. 3 ; see color plate at the back of the book). Indirect calorimetry has the advantage of mobility and low equipment cost and is frequently used in clinical settings to assess patients’ energy requirements. Indirect calorimetry also provides quantitative information about the types of substrates that are oxidized [19 ]. The pretesting environment impacts the measurement of RMR. Outpatient-test experimental conditions have been shown to overestimate RMR by approximately 8% compared with inpatient measurements of RMR [20
eBook - PDF- Eric S. Rawson, Stella Volpe, Eric S. Rawson, Stella Volpe(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
BMR is the amount of energy that 6 Nutrition for Elite Athletes is expended, or used, by the body purely to live and exist. Many internal body pro- cesses contribute to the BMR such as breathing, pumping of the heart to circulate blood, and thinking. Another version of the BMR is the resting Metabolic Rate (RMR). This rate is almost the same as the BMR, but slightly higher because it accounts for waking rest, which requires slightly more calories than the pure basal rate; that is, the (RMR) is the energy required to lie quietly in bed. In general, the values can be considered equivalent because the RMR is only approximately 5% to 10% higher than the BMR for any given individual. For this reason, it is not necessary to differentiate between the two when referencing the total energy expenditure equation. However, it is neces- sary to select one term and stay consistent in your calculations. For uniformity, we will use BMR throughout this chapter. There are many methods to determine the BMR, including using direct calorim- etry (Dauncey 1980), indirect calorimetry (Reeves and Capra 2003), or the doubly labeled water method (Plasqui and Westerterp 2007). The three methods are con- sidered to be within 3% of the actual BMR when performed under ideal conditions (Schoeller and van Santen 1982). Because these techniques may not be amenable to clinical settings, several equations have been developed to determine BMR that take into account an individual’s age, sex, height, and weight. These equations are much easier to use than the aforementioned methods because they do not require time, money, or expensive machinery to conduct. However, these equations are much less accurate and must be understood as estimations rather than absolute values (Reeves and Capra 2003). Each of these equations may vary by up to 10% from the actual BMR of the tested individual (Henry 2005). However, the simplest way to calcu- late BMR is based solely on a person’s weight.
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