GLOSSARY

Brozek Equation is a classical density-to-fat conversion associated with Brozek and colleagues. It is a model-based transformation and should not be treated as universally interchangeable with other equations.

Densitometry relates body mass to estimated body volume, then uses a model to estimate fatness. Underwater weighing and air-displacement plethysmography obtain volume differently and require their own corrections. Lung gas, clothing, preparation and procedural assumptions can affect the estimate. A density-to-fat equation also assumes particular properties of fat-free tissue. These methods can be useful, but results should not be assumed interchangeable with DXA, bioimpedance or a direct anatomical measurement.

Body-composition models divide the body into components according to a defined level. A two-component model often separates fat mass from fat-free mass. Adding measured water or mineral information can reduce some assumptions in more complex models, but no model removes all error. Molecular, cellular and tissue descriptions are different ways of organizing the same body. Before comparing results, identify the model, measured variables and assumptions rather than treating all reported components as directly measured anatomical tissues.

Fat-free mass includes water, protein, minerals and other nonfat constituents. It therefore includes organs and bone as well as skeletal muscle. Lean body mass, fat-free mass and lean soft tissue can have different technical meanings, although terms are sometimes used loosely. A short-term rise in a device's lean-mass estimate can reflect hydration or glycogen rather than new contractile protein. Check the device definition and testing conditions before calling a change muscle growth.