leanmass

Lean mass, commonly referred to as lean body mass (LBM), is the portion of total body weight that remains after subtracting fat mass. It comprises skeletal muscle, bone, organs, connective tissue, and body water. Some definitions distinguish lean mass from fat-free mass, noting that essential fat (required for normal physiological function) may be treated as part of lean mass or as a separate component depending on the measurement approach.

Measurement of lean mass is performed with several methods, each with pros and cons. Dual-energy X-ray absorptiometry (DEXA) is widely used in research and clinical settings to estimate body composition, including Lean Mass. Bioelectrical impedance analysis (BIA) offers portable, quick assessments but can be less accurate and affected by hydration. Other methods include hydrostatic (underwater) weighing, air displacement plethysmography (Bod Pod), and imaging techniques such as MRI or CT scans.

Lean mass is a key variable in fitness, athletics, and health monitoring. It is often tracked to assess responses to resistance training, dieting, or medical interventions. Higher lean mass is associated with greater resting metabolic rate, strength, and functional capacity, and it can influence clinical outcomes related to aging and chronic disease.

Factors influencing lean mass include age, sex, hormonal status, physical activity, and nutrition. Resistance training is the primary driver of increases in lean mass, with adequate protein intake and sufficient total energy supporting gains. Typical guidance for athletes emphasizes progressive overload and protein intake around 1.6–2.2 grams per kilogram of body mass per day, along with adequate rest.

Limitations include measurement variability across methods, hydration effects on some assessments, and the fact that lean mass is not a direct measure of muscle quality or function.