GLOSSARY

Lean Mass describes a lean body compartment whose technical definition depends on the method. Lean body mass, fat-free mass and lean soft tissue should not be treated as perfectly interchangeable labels.

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.

Skeletal muscle contributes force and movement, but muscle quantity and performance are not identical. Training quality, neural adaptations, architecture and task specificity matter alongside tissue mass. Resistance exercise and adequate nutrition can support muscle gain or preservation, while energy restriction may make this harder. A larger measured lean compartment does not automatically demonstrate a larger muscle compartment. Interpret body-composition changes alongside strength, function and the demands of the sport rather than using mass alone as the outcome.

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.