Question

I your own words EXPLAIN two methods for measuring physical activity, exercise behavior, or estimated energy expenditure. What are the strengths and weaknesses of each method?

Answer 1

DLW or doubly labeled water method : Doubly labeled water is in which Hydrogen and Oxygen have been partly or completly replaced with an isotope for tracing purpose. DLW method uses stable isotopes of ¹⁸O and ²H (deuterium) This method measures a subjects carbon di oxide production during the interval between first and last body water sample, it is based on the princple that the two isotopes equilibrate with total body water and are eliminated diffrently from the body. ²H leaves the body as water while ¹⁸O leaves the body as water and carbon di oxide, therefore carbon di oxide elimination can be calculated by subtracting ²H elimination from ¹⁸O elimination. Advantages of this method are there are no subject compliance except giving urine or saliva sample, there are no fear of equipment breakage and can be used to validate other feild technique. Major draw back are the cost of ¹⁸O-labeled water and the technical analysis of isotope, and there are only few labarotary having mass spectrometer and sample preparation system are limited.

In Direct Calorimetry Method : Calorimetry is way of determining change in enegy of a system by measuring the heat exchange of the system with the surroundings. Indirect calorimetry is a type of body calorimetry where all gas exchange are continously monitored and can be used to determine energy expenditure, This technique relies on the measurment of inspired and expired gas volume and the concentration of oxygen and carbon di oxide, the results are calculated using modified Weir's equation. The main advantage of this system are it is non invasive method and it can allow tha assesment of energy expenditure on feild through the use of ambulatory metabolism system.The main drawbacks are not all technicians are trained in use and intrepretation of the results, equipments are fairly costly not always available, new tecnology now integrated into ventilator.