GLOSSARY

DXA Bone Mineral Content is the bone-mineral amount estimated by DXA. It differs from total living bone mass and from mineral content divided by projected bone area.

DXA estimates fat, lean soft tissue and bone mineral from the attenuation of X-rays at different energies. It is not a direct chemical dissection of the body. Food, hydration, recent exercise, positioning, software and analysis boundaries can affect longitudinal comparisons. The same device and a standardized protocol improve interpretation. A small apparent lean-mass change may fall within normal variation or reflect glycogen and water, so compare it with the method's precision and relevant performance information.

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.

For example, compare repeated DXA assessments using the same preparation, positioning and analysis approach. An apparent lean-tissue change following a carbohydrate-heavy period should be checked against water and glycogen effects. The result can support a longer-term evaluation without being treated as direct proof of muscle hypertrophy or an instruction to pursue a lower body-fat value.

Bone mineral content is an amount of mineral, whereas DXA bone mineral density commonly expresses mineral content relative to projected area. Neither is identical to the total mass of living bone, which also contains organic material and water. Interpretation depends on site, age, reference population and clinical context. Athletes need adequate energy and relevant nutrients as well as suitable loading. A single body-composition scan should not be used to make an independent diagnosis or to prescribe treatment without appropriate assessment.