Assessment of Human Body Composition Methods and Limitations
This chapter describes the physical bases of the methods for the assessment of body composition and outlines the characteristics of each technique focusing on validity, applicability, and precision of estimation of a body component for an individual. In most body composition studies, validity encompasses the concepts of accuracy and precision besides others. The most commonly recorded anthropometric data are body mass, standing height, specific body segment lengths, breadths and circumferences, skinfold thickness, and, currently, the measurement of subcutaneous fat with ultrasound. Bioimpedance provides indirect information on body composition by measuring resistance (R), which is the opposition to the flow of an alternating current through intra- and extracellular ionic solution, and reactance (Xc), which is the capacitive component of tissue interfaces, cell membranes, and organelles of the body. The isotope dilution technique is a method to measure total body water (TBW) and extracellular fluid (ECF).