Lean Body Mass (Boer)
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kg
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What is Lean Body Mass?
Lean Body Mass (LBM) is the weight of everything in your body except fat — including muscle, bone, organs, water, and connective tissue. It's a more meaningful health metric than total body weight because it separates the "useful" mass (muscle, bone) from stored fat.
LBM is used in medicine to calculate drug dosages, determine protein requirements, set fitness goals, and monitor body composition changes over time. Athletes track LBM to ensure they're building muscle and losing fat simultaneously.
The Four LBM Formulas
Boer (1984) — Male: LBM = 0.407W + 0.267H − 19.2
Boer (1984) — Female: LBM = 0.252W + 0.473H − 48.3
James (1976) — Male: LBM = 1.10W − 128(W/H)²
James (1976) — Female: LBM = 1.07W − 148(W/H)²
Hume (1966) — Male: LBM = 0.3281W + 0.3393H − 29.5336
Hume (1966) — Female: LBM = 0.2969W + 0.4135H − 43.2933
Peters (children): LBM = 3.8 × (0.0215 × W^0.6469 × H^0.7236)
W = weight in kg, H = height in cm
Which Formula Should I Use?
The Boer formula is considered the most accurate for average-weight adults and is the most commonly used in clinical settings. The James formula can underestimate LBM in obese individuals. The Hume formula performs well across a wide range of body types. The Peters formula is specifically designed for children and adolescents under age 14.
Tips for Improving Lean Body Mass
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Resistance Training
Progressive overload with weights is the most effective way to increase skeletal muscle mass and therefore LBM.
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Protein Intake
Consume 1.6–2.2g of protein per kg of LBM daily. Spread intake across meals for optimal muscle protein synthesis.
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Sleep & Recovery
Muscle repair and growth primarily occur during sleep. Aim for 7–9 hours. Poor sleep elevates cortisol and impairs gains.
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Track Trends
LBM is more meaningful than scale weight. If weight stays flat but LBM rises, you're gaining muscle and losing fat — a great outcome.
Frequently Asked Questions
What is the difference between LBM and muscle mass?
Lean Body Mass includes everything except fat — skeletal muscle, smooth muscle, bone, water, organs, and connective tissue. Skeletal muscle is typically about 40–45% of total body weight in healthy adults. LBM is a broader category; muscle mass is a subset of it. Some calculators use "lean mass" and "muscle mass" interchangeably, but they are technically different.
Can LBM change even if weight stays the same?
Yes — this is called "body recomposition." If you gain 2kg of muscle and lose 2kg of fat, your scale weight stays the same but your LBM increases and fat decreases. This is a desirable outcome for most fitness goals and is why measuring LBM is more informative than tracking total body weight alone.
Why do different formulas give different results?
Each formula was derived from different population studies with different demographics, ages, and measurement methods. The Boer formula used cadaver studies; the James and Hume formulas used different regression analyses. No single formula is perfectly accurate for everyone — the Boer formula has the broadest validation data for adults and is generally recommended.
How is LBM used in medical dosing?
Many medications — especially anesthetics, antibiotics like aminoglycosides, and chemotherapy drugs — are dosed based on lean body mass rather than total body weight. This is because drug distribution in the body is more closely related to lean tissue volume than to total weight. Using total weight in obese patients can lead to overdosing.
