III
Techniques of Body Composition Assessment
PART III BEGINS WITH AN OVERVIEW in Chapter 4 of the military's use of body composition standards to enhance readiness, promote fitness, and maintain appearance. Body fat standards vary by age, gender, and branch. The military relies primarily on body mass index to predict percentage body fat. Equations incorporating anthropometric measurements are then used to determine percentage body fat in those who fail the initial screen. While hydrodensitometry has been the criterion method for validating these equations, other assessment techniques are being explored.
Imaging methods for studying body composition at the tissue-system level are explored in Chapter 5. Computerized axial tomography and magnetic resonance imaging/spectroscopy measure total-body skeletal muscle mass and adipose tissue. They allow clear visualization of the boundaries between adipose tissue, muscle, and bone and quantification of all major tissue-system level components: adipose tissue, skeletal muscle, bone, visceral organs, and brain. The images of these components are analyzed to estimate tissue-and organ-level body composition, and algorithms are applied to estimate total tissue-system volume.
Dual-energy x-ray absorptiometry, discussed in Chapter 6, measures bone mineral content and bone mineral density. As a means of body composition measurement, x-ray attenuation distinguishes bone mineral, nonbone lean tissue,
and fat and can be used to evaluate regional body composition. While soft tissue measurements are not accurate, this method may become the criterion method of assessing body composition because of the precise data it produces and its independence from underlying assumptions.
As presented in Chapter 7, bioelectrical impedance analysis measures current flow through the body noninvasively to generate equations that are validated against other body composition assessment methods. This method is based on the assessment of total body water, so its utility is affected by differences in hydrational status.
