Advanced methods of body composition analysis:
Bioelectrical impedance (BIA);
In bioelectrical impedance analysis (BIA), electric current is passed through the body and its impedance(resistance and reactance) is measured to estimate the total body water.
''Bioelectrical'' is defined as the interaction of body with electric current while ''impedance '' is the interaction of body with electric current encountered in the form of the opposition to the passage of the current encountered in the form of resistance and reactance . Resistance is the given opposition to the passage of current by body fluids.
While on the other hand, reactance is the opposition provided by cell membranes (imperfect capacitors). In BIA method, impedance is measured that gives an estimate of total water content of the body, which can be used to calculate FM and FFM by other tools.
Ideally, the test is performed after the fasting, 30min after voiding under normal hydration ( dehydration can cause significant error ). It is a simple, rapid, reliable, easy to use and affordable method for body composition analysis. Less expertise is required and is applicable to both genders.
It can be used in large studies and can integrate in out patients settings. However, some limitations are associated with this technique as instrumentation required for the analysis is complex. The result of this method is affected by different factors including:
- Hydration levels
- skin temperature
- Exercise
- Meals
- Caffeine and alcohol consumption
Apart, the predictive equations may not be applicable to certain population groups ( pregnant women, therapies, young children ). It determines fat from body part attached to device, thus, gives in accurate measurements for persons having unbalanced body fat distributions.
Densitometry :
Measurement of total body density, gives an idea of body composition. Body volume is measured by hydro densitometry ( a classic approach of determining body composition through under water weighing ).
A new alternate is displacement of plethysmography, the technique which account for volume of air displaced by the object.
It is pertinent to mention that FM and FFM have different specific densities. Hydro densitometry also called as hydrostatic underweight weighing/hydrostatic testing is based on Archimedes principle which states that " the buoyant force ( pressure exerted on a submerged object by the fluid ) on a submerged object".
It is used to measure percent body fat in human body because the specific density of FM and FFM is constant . Lean tissue i.e muscle tissue and bones are denser than water, while fat tissue have lower density than water. Resultantly, the muscles shrinks and fat floats and an individual with higher body fat will weigh less when underwater and be more buoyant.
Contrarily, the person with higher muscle mass weigh more underwater and is less buoyant. Following formula is used to calculate body density
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