What is lean body mass?

Lean body mass refers to the total weight of all body components excluding fat. This includes not only the muscles but also bones, organs, and water that is not stored as fat. Lean body mass is an important measure in body composition because it provides insight into the metabolic weight of the body and is often a focus in fitness and health assessments. Understanding lean body mass helps in evaluating an individual's overall health and developing tailored fitness programs.

The other options focus on aspects that do not encompass the full definition of lean body mass. For example, fat tissue is explicitly the opposite of lean body mass, while muscular tissue alone does not account for the bones and organs that are also part of lean body mass. Additionally, extracellular water is just a component of lean body mass and does not represent the entirety of non-fat body components. Thus, the understanding framed in the correct choice captures the comprehensive nature of what lean body mass entails.