Question 1

What is lean body mass (LBM) and why does it matter?

Accepted Answer

Lean body mass (LBM) is the total body weight minus fat mass — it includes muscle, bone, water, connective tissue, and organs. LBM is a critical metric in clinical medicine (for drug dosing), sports science (for performance), and general fitness. A higher LBM relative to total weight indicates better body composition and is associated with higher metabolic rate, better glucose regulation, and lower chronic disease risk.

Question 2

What is the difference between the Boer, James, and Hume formulas?

Accepted Answer

All three use only weight, height, and sex, but differ in derivation. Boer (1984) is the most widely validated across diverse populations and is WHO-preferred for general clinical use. James (1976) is the pharmaceutical standard for calculating drug doses and is especially used in critical care. Hume (1966) was derived from cadaver studies and is a historical reference. At normal BMI values all three agree closely; differences emerge at extreme weights or heights.

Question 3

What is FFMI and what is a natural athlete limit?

Accepted Answer

Fat-Free Mass Index (FFMI) = LBM (kg) ÷ Height (m)². Normalized FFMI corrects for height, standardizing to a 1.80 m reference. According to Kouri et al. (1995), the documented upper limit for natural (drug-free) male athletes is approximately FFMI 25–26. Normalized FFMI above 26 in men, or above 22 in women, is considered near or beyond the natural ceiling and warrants scrutiny. FFMI requires an accurate body fat percentage measurement.

Question 4

Which LBM method is most accurate?

Accepted Answer

The Body Fat Method (LBM = weight × (1 − BF%)) is the most accurate if you have a measured body fat percentage from DXA, DEXA, or a calibrated skinfold protocol. For general estimation without BF% measurement, the Boer formula is the most clinically validated. The Formula Comparison tool averages Boer, James, and Hume, which is more robust than any single formula at the population level.

Question 5

How much protein do I need to maintain lean body mass?

Accepted Answer

For maintenance of existing lean mass, current consensus (ACSM/AND/DC 2016) recommends 1.2–1.6 g of protein per kg of LBM per day. For muscle gain, the evidence-based range is 1.6–2.2 g/kg LBM/day. For fat loss while preserving LBM, a higher intake of 2.0–2.4 g/kg LBM is recommended combined with resistance training (Morton et al. 2018).

Question 6

Can lean body mass improve with age?

Accepted Answer

Yes. Sarcopenia (age-related muscle loss) is not inevitable. Resistance training 2–3 times per week consistently preserves and even increases LBM at any age. Progressive overload combined with adequate protein (≥ 1.6 g/kg LBM/day) and vitamin D sufficiency are the three most evidence-backed interventions. Even adults over 70 respond measurably to resistance training (Peterson et al. 2011, JAMA).

Question 7

Why do the three formulas sometimes give different results?

Accepted Answer

Each formula was derived from different population samples and regression methods. Differences are small at normal BMI (18.5–25) but widen at extremes. At very high body weight, James can underestimate LBM. At very low height, Hume may produce negative or implausible values. This is why the Formula Comparison mode shows the spread — a wide spread (> 3 kg) suggests you are outside the normal range where all formulas are most reliable, and a DXA scan would give a definitive answer.

Type	Description
Formule Boer	Formule de LBM la plus courante
Formule James	Estimation de James (1976)
Formule Hume	Estimation de Hume (1966)

Type	Description
Formule Boer	Formule de LBM la plus courante
Formule James	Estimation de James (1976)
Formule Hume	Estimation de Hume (1966)

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