Resting Metabolic Rate (RMR)

Resting Metabolic Rate (RMR) How Do You Measure ENERGY EXPENDITURE?

Metabolic Rate in Various Conditions • Basal Metabolic Rate (BMR) Minimum energy required to sustain life (Measured when Waking State with No Food & No Movement) • Resting Metabolic Rate (RMR) Combination of… Basal Metabolism (waking state) Sleeping Metabolism Arousal Metabolism • Exercise Metabolic Rate Metabolism during Exercise + RMR

How Do You Measure Metabolic Rate? Substrate (CHO or Fat) + O2 + Energy (ATP)  CO2 + H2O + Energy (ATP) + Heat Method #2 INDIRECT CALORIMETRY Method #1 DIRECT CALORIMETRY

Method #1DIRECT CALORIMETRY Total Energy from Metabolism... ~40%  ATP ~60%  Heat So… if you measure your body’s heat production, you can estimate energy production!

DIRECT CALORIMETRYHow Does It Work? Insulated Chamber Heat Exchanger Water flow in the heat exchanger The difference in the temperature of water entering and leaving the chamber reflects the person’s heat production.

DIRECT CALORIMETRYProblems • Expensive • Not applicable in most activities • Highly impractical for large-scale studies • Very few pieces of equipment in nation So…Method #2 

Method #2INDIRECT CALORIMETRY Complete Combustion of Food IS Achieved at the Expense of O2 Molecules. So… if you measure your oxygen uptake, you can estimate energy production!

INDIRECT CALORIMETRYHow Does It Work? Oxygen Uptake = (VO2 IN) – (VO2OUT) O2 Inspired O2 Expired

INDIRECT CALORIMETRYHaldane Transformation Assumptions • Ambient Air • FIO2 = 20.93% = 0.2093 • FIN2 = 79.04% = 0.7904 • FICO2 = 0.03% ~ 0 (ignore it) • FIN2 + FIO2 = 1 • FEN2 + FEO2 + FECO2 = 1 • VI*FIN2 = VE*FEN2 (N2 is inert gas)

INDIRECT CALORIMETRYHaldane Transformation VO2 = (VI*FIO2) – (VE*FEO2) VI*FIN2 = VE*FEN2 VE*FEN2 FIN2 VE* [1 – (FECO2 + FEO2)] FIN2 1 – (FECO2 + FEO2) 0.7904 VI = VI = VO2 = VE X 0.2093 – FEO2

Respiratory Quotient (RQ) CO2 produced O2 consumed Each substrate has its own RQ value. (carbohydrates (1.0) vs fatty acids (0.7)?) RQ = At the CELL

Carbohydrate (Glucose): C6H12O6 + 6O2 6CO2 + 6H2O + Energy RQ = 6CO2 / 6O2 = 1.00 Fat (Palmitic Acid): C16H32O2 + 23O2 16CO2 + 16H2O + Energy RQ = 16CO2 / 23O2 = 0.70 RQ for CHO and FAT

What about Protein? • Protein is metabolized as either fat or carbohydrate and is therefore difficult to separate from the other two • Protein consumption is a small percentage of total metabolism during normal conditions and can be ignored

Respiratory Exchange Ratio (RER) CO2 produced O2 consumed Actual gas exchange (RER) at the lungs can be greater or less than the RQ at the cell. It can range from slightly below 0.7 all the way to around 1.5 (lots of non-metabolic CO2) (hyperventilation vs hypoventilation?) RER = At the LUNGS

How Do You Use RQ or RER? Assuming RQ = RER, you can estimate the energy produced per liter of O2. e.g. RQ = 0.85  4.86 kcal/LO2 (Utilizing 50.7% CHO & 49.3% Fat)  Table 4.4

Comparing RMR • Absolute Oxygen Uptake (in LO2/min) more muscle mass  higher absolute VO2 Not able to compare 300 lbs football player and 130 lbs X-country runner • Relative Oxygen Uptake (in mlO2/kg/min) Eliminates some of the differences in muscle mass by using body mass (body composition is unaccounted for)

Metabolic Equivalent (MET) A MET is defined as a multiple of the Resting Metabolic Rate. e.g. If RMR (1 MET) = 3.6 mlO2/kg/min, Work requires 7.2 mlO2/kg/min of O2 uptake = 2 METS (# of METS in different activities?)

STPD Correction Factor STPD: Volume of Gas expressed under Standard Conditions of • Temperature (273K or 0°C) • Pressure (760 mmHg or 1 atm) • Dry (no water vapor) 273K PBAR – PH2O 273K + TA (in °C) 760 mmHg (hot, wet condition vs cold, dry condition?) STPDCF = X

Resting Metabolic Rate (RMR)