Resting Metabolic Rate Lab - Exercise Physiology PDF

**BACKGROUND** **Part 1. Resting Metabolic Rate** The minimum level of energy required to sustain the body's vital functions in the waking state is the basal metabolic rate (BMR), which is usually expressed in kcal/day and makes up the majority of a person's total daily energy expenditure (TDEE;...

**BACKGROUND** **Part 1. Resting Metabolic Rate** The minimum level of energy required to sustain the body's vital functions in the waking state is the basal metabolic rate (BMR), which is usually expressed in kcal/day and makes up the majority of a person's total daily energy expenditure (TDEE; the amount of kcals someone burns in a day). TDEE is comprised of three parts BMR (60-75%), the thermic effect of feeding (TEF, 10%), and activity thermogenesis (AT, 15-30%). Activity thermogenesis can further be delineated into two parts exercise activity thermogenesis (EAT) and nonexercise activity thermogenesis (NEAT). True BMR is difficult to obtain because the subject must sleep for at least 8 h and fast for at least 12 h. This typically requires staying overnight in a metabolic laboratory. As a result, most researchers measure the RMR. RMR still requires resting and fasting, but it does not necessitate staying overnight in the lab. The currently accepted guidelines for RMR assessment as set forth by Fullmer et al., 2015 are: 1. Fast from all calorie-containing food and beverages for ≥ 8 hours 2. Rest in a dark room with no distractions for 30 minutes prior to the test 3. Abstain from any exercise for at least 24 hours 4. No caffeine, or other stimulant, consumption for ≥ 12 hours prior to the test As long as the preceding conditions are met, RMR can be assessed at any time of day. However, for best results, and to aid in participant comfort, this test is typically conducted in the morning. This way, the majority of the fasting hours will occur overnight while the participant is asleep. RMR is typically assessed through a method known as **indirect calorimetry**. This technique utilizes specialized metabolic carts that assess the volume of carbon dioxide (VCO~2~) being produced and oxygen (VO~2~) being consumed during each breath. It uses the knowledge that our atmosphere contains 20.93% oxygen, 0.03% carbon dioxide, and 79.04% nitrogen and that the concentrations of these gases change in our expired breath. The amount of oxygen decreases as we consume oxygen, whereas the amount of carbon dioxide increases, and nitrogen remains unchanged in our expired breath. These carts are then able to estimate RMR through the following Weir equation: RMR = 1.44 × \[(VO~2~ ×3.9) + (VCO~2~ ×1.1)\] The consumption of oxygen and the production of carbon dioxide thus become functions of the fractions of these gases in the air and the expired breath, as well as the volume of air per breath. Therefore, metabolic carts measure only three critical components---the percentages of oxygen and carbon dioxide in the expired breath and the volume of that breath. As we know from physics, the volume of a gas is affected by both temperature and pressure, which means the local barometric pressure and ambient temperature are important for these measurements. Many metabolic carts can measure expired gases, ventilation, and temperature and pressure for every breath, whereas others use a small mixing chamber to average the numbers over a discrete period of time. For best results, the data would be taken using one-minute averages. Watch the following videos for examples and explanations of RMR Testing: - BMR test with RER at Univ. Florida: . - RMR test with REEVue or CardioCoach (like our MetaCheck device): & - RMR test with Miller Method: - Explanation of BMR & TDEE: **Part 2. Estimating Resting Metabolic Rate** As directly assessing RMR can be cumbersome for the participant or practitioner, costly (some devices can cost \>\$60,000), and requires trained technicians to run and analyze the test, the use of prediction equations to estimate RMR has become much more commonplace in field settings. These prediction equations utilize various metrics such as height, weight, body composition (amount of fat mass and muscle mass), age, and sex to estimate an individual's RMR. While a great number of prediction equations exist, as shown by Rodriguez et al. (2022), the number one determining factor for determining the validity of a selected prediction equation is the population in which it was developed. It is often believed that equations that use body composition metrics, such as fat mass or muscle mass, are more accurate. However, this is not the case. A body weight-based equation being utilized in the right population will outperform a body composition-based equation in the wrong population. Table 1. displays a number of common equations and the populations in which they were developed. Once RMR is estimated using the proper equation, RMR is converted to TDEE by my of an **activity factor (AF)**. An AF is a method of estimating how active a person is **ON AVERAGE** within their daily life. This is often defined using the following chart: **Activity Factors for Various Levels of Activity** - ***Sedentary ---** desk job and little to no exercise (multiply by 1.2)* - ***Lightly Active ---** light exercise/sports 1--3 days/week (multiply by 1.375)* - ***Moderately Active ---** moderate exercise/sports 3--5 days/week (multiply by 1.55)* - ***Very Active ---** hard exercise/sports 6--7 days/week (multiply by 1.725)* - ***Extremely Active ---** hard daily exercise/sports and physical job or training (multiply by 1.9)* Thus, the equation for estimating TDEE would be **TDEE = RMR × AF**. Note, this would be to estimate the number of kcals an individual would need to consume to **maintain** their weight. If the goal was weight loss, they would need to consume below this number and vice versa for weight gain. Table 1. Selected RMR estimation equations and the populations in which they were developed --------------------------------------------------------------------------------------------- -------------------------------- ---------------------------------------------------------------------------------------------------- **Name** **Population** **Equation** Body Mass Based Equations Harris-Benedict (Males) Healthy inactive men and women (13.752 × BM (kg)) + (5.003 × Height (cm)) -- (6.755 × Age (y)) + 66.473 Harris-Benedict (Female) (9.563 x BM (kg)) + (1.850 x Height (cm)) -- (4.676 x Age (y)) + 655.096 Mifflin-St. Jour (9.99 x BM (kg)) + (6.25 x Height (cm)) -- (4.92 x Age) + (166 x Sex) -161 DeLorenzo High activity athletes (3h/d) (9 x BM (kg)) + (11.7 x Height (cm)) - 857 Ten Haaf and Weijs Generally active 0.239\[(49.94 × BM (kg)) + (2459.053 × H (meters)) -- (34.014 × age) + (799.257 × sex) + 122.502\] Fat-Free Mass Based Equations Cunningham Healthy inactive men and women (22 x FFM (kg)) + 500 Owen Subjects with obesity (22.3 x FFM (kg)) + 290 Mifflin-St. Jour Healthy inactive men and women (19.7 x FFM (kg)) + 413 Ten Haaf and Weijs Generally active 0.239\[(95.272 x FFM (kg)) + 2026.161\] Muller Healthy inactive men and women (13.587 x FFM (kg)) + (9.613 x FM (kg)) + (198 x Sex) -- (3.351 x Age) + 674 For sex: Males = 1 Females = 0 **Part 3. Respiratory Exchange Ratio and Respiratory Quotient** One important measurement that can be accomplished with knowledge of VO~2~ and VCO~2~ is the type of fuel being used. On this point, the respiratory quotient (RQ) or respiratory exchange ratio (RER) provides information regarding the macronutrient being oxidized at any given time during steady state. RQ and RER differ only in the place where they are measured---that is, at the cellular level and in the expired gases, respectively. For the purposes of this lab, we will refer to RER. Both metrics are calculated using the same equation: VCO~2~ / VO~2~. - RQ (at the cellular level) = [\$\\frac{VCO2}{VO2}\$]{.math.inline} - RER (expired gasses measured at the mouth) = [\$\\frac{VCO2}{VO2}\$]{.math.inline} These ratios measure the quantity of CO~2~ produced in relation to the quantity of O2 consumed. Because of inherent differences in the chemical composition of carbohydrate, fat, and protein, each requires a different amount of oxygen to completely oxidize the molecules to the end products of bioenergetics---ATP, CO~2~, and H~2~O. Thus, because the caloric equivalent for oxygen differs somewhat depending on the nutrient oxidized, one must know the RER and the amount of oxygen consumed to precisely estimate the body's energy expenditure in kcal/min (see Table 2). The number of kilocalories produced for each liter of oxygen consumed (kcal/L) depends on the substrate being utilized or RER. The RER is 1.0 for carbohydrate, 0.70 for fat, and 0.82 for protein. The protein contribution to energy production is low (generally less than 5%). To gain a true understanding of the contribution of protein to energy production, urine must be collected because urea is the metabolic end point for the amino groups of amino acids that have been oxidized. However, due to the complexity of analysis and the inconvenience of collecting urine, as well as the small contribution of protein to energy expenditure, RER is generally considered to be nonprotein RER. Therefore, at any given time, a mixture of carbohydrate and fat is being oxidized by the mitochondria for energy needs, and the kilocalories produced per liter of oxygen consumed varies accordingly. Table 2 reflects the percentage of fat and carbohydrate contributing to energy production at a given RER. Normally, people who consume a diet of mixed carbohydrate and fat have an RER value of about 0.85 at rest, which means that for every 1 L of oxygen consumed, approximately 4.86 kcal are produced. In measuring resting metabolic rate (RMR), the researcher must have a measure of oxygen consumption and an RER value for each minute of the measurement period in order to determine the kilocalories produced per minute (see the accompanying highlight box for a sample calculation). Many exercise physiology students never realize why carbohydrate has an RER of 1.0 and fat has an RER of 0.7. Here are the equations for the overall oxidation of carbohydrate and fat:  Table 2 -- Selected RER Metrics --------------------------------- ------------- ------- ------- RER Kcal/L O~2~ \%CHO \%Fat 1.00 5.047 100 0 0.97 5.010 90.4 9.6 0.93 4.961 77.4 22.6 0.90 4.924 67.5 32.5 0.87 4.887 57.5 42.5 0.83 4.838 43.8 56.2 0.81 4.813 36.9 63.1 0.78 4.776 26.3 73.7 0.75 4.739 15.6 84.4 0.72 4.702 4.8 95.2 0.70 4.686 0 100