Lean Body Mass is collective terms for the non-fatty components of the body and includes bone, water, muscle, organs, and tissues. It is also referred to as lean tissue. These tissues are metabolically active, burning calories for energy, while body fat does not. It is calculated by subtracting the weight of the fatty tissue from the total weight of the body.
Most fitness / wellness enthusiasts aim to maintain their lean body mass while at the same time reducing their fat mass, thereby reducing their overall body fat percentage, and providing the 'toned' appearance that many strive for. Owing to muscle being denser in weight than fat, LBM is an important measure for people on weight management programmes, who can often be fixated with weight as the only success metric, and who can get frustrated when the weighing scale doesn't appear to move much despite their hard work. LBM and Body Fat percentage are additional success metrics that should also be considered that can help overcome any weight frustration.