First of all ... what is lean mass? Explaining it is important, since many people have confused ideas about its meaning:
the lean mass or LBM (from the English Lean Body Mass) represents all that remains of the organism after having deprived it of the storage fat (adipose tissue).
This datum, which has nothing to do with the ideal weight, differs slightly from another anthropometric parameter, called fat-free lean mass:
the lean alipidic mass or FFM (from the English Fatty Free Mass) represents all that remains of the organism after having deprived it of all its lipidic component, including the primary or essential fat (which protects the internal organs, constitutes the bone marrow, mammary glands and is present in various tissues).
The lean mass, therefore, is given by the contribution of bones, teeth, muscles, internal organs, connective tissue and essential fat. The distinction with the lean alipidic mass is important, since the primary fat is essential for the health of the individual and cannot be affected, if not minimally, by weight loss; it constitutes about 3% of the male body mass and 12% of the female body mass.
Fat mass (FM, from English Fat Mass) represents the total amount of lipids that can be extracted from the human body (primary fat + storage fat). For what has been said so far, a fat mass less than 3% in men and 12% in women is not compatible with good health and in the most drastic cases even with the life of the individual.
The determination of lean mass in vivo can take place according to different methodologies that differ in practicality, accuracy and costs (plicometry, bioimpedentiometry, body circumferences, Dexa, creatinine, magnetic resonance, CT, K40 and ultrasound). A simple and immediate method consists in calculating the lean mass starting from the height and the individual weight:
James's formulas:
Lean mass kg (man) = [1.10 x W (kg)] - 128 x {W2 / [100 x H (m)] 2}
Lean mass kg (woman) = [1.07 x W (kg)] - 148 x {W2 / [100 x H (m)] 2}
These are obviously approximate equations, useful for obtaining an estimate of the lean mass in sedentary individuals but completely unreliable in the evaluation of an athlete. Its value is in fact influenced by muscle mass (which normally represents about 50% of LBM) and by bone mass (about 20%). Consequently, a sportsman with strong bones and highly developed muscles will have a significantly higher lean mass than a sedentary person of equal weight.
The lean mass, if calculated in a precise and reliable way, provides excellent information on the basal metabolism (clearly better than those obtained based on the height of the individual). Among the many formulas, we recall that of Katch and McArdle, according to which the basal metabolism is equal to:
370 + (21.6 * LBM)
Observing the aforementioned formula, it is evident that the basal metabolism is directly proportional to the lean mass of a subject. Since its value is mainly influenced by muscle tissue, the more muscles we have and the more calories we consume during the day, regardless of age, thyroid function and level of physical activity. In fact, muscle is a living tissue. in continuous renewal and with metabolic demands clearly superior compared to adipose tissue (almost ten times). To lose weight it is therefore advisable to go through an increase in lean mass, following an appropriate diet and a regular exercise program.
