In body composition, what is lean mass typically composed of?

Lean mass refers to the collective weight of all tissues in the body that are not classified as fat. This includes muscle mass, bones, organs, blood, and water in the body. Therefore, the correct understanding of lean mass encompasses all tissues that do not contain fat, making it a broader category than just muscle or other individual components. Recognizing that lean mass includes a variety of tissues highlights its importance in overall body composition and health.

In contrast, the other options narrow the definition of lean mass incorrectly. For instance, fat tissue only refers solely to adipose tissue, excluding all forms of lean mass. Similarly, only muscle mass would disregard essential components such as bones and organs that are vital for understanding body composition. Lastly, while muscle, bone, and water do comprise parts of the lean mass, they don't encompass all non-fat tissues, making a more comprehensive definition necessary for clarity. Understanding that "all tissue excluding fat" makes up lean mass provides a complete picture relevant to health and fitness assessments.