What is lean mass?

Lean body mass is your total mass excluding fat mass. Lean mass includes muscle, bones, organs, and water. Skeletal muscle mass is the largest component in adults and accounts for about 40% of your total body weight.

Healthy lean mass is important for healthy aging for many reasons, including supporting strong bones and a healthy metabolism.

Tracking lean body mass over time is a great way to see gains in muscle mass that come from training. Since bones, organs, and water weight change very little in adults over time, relative changes in lean mass can be associated with muscle mass.