What is the "fat-free mass index" and is it a better measure than BMI?

The fat-free mass index (FFMI) is total lean body mass in kg divided by height in meters squared, analogous to BMI but for muscle mass rather than total weight, with reference values showing that natural (non-anabolic steroid) men over 40 rarely exceed FFMI of 22–23 through training alone, making FFMI above 25–26 in a man claiming natural status physiologically implausible and likely indicating exogenous anabolic steroid use (Kouri et al., Clin J Sport Med, 1995).

FFMI has two practical applications for men over 40: (1) as a better body composition target than BMI (targeting FFMI of 19–22 instead of BMI of 22–25 aligns body composition goals with muscle mass rather than just weight); (2) as a reference point for assessing whether a man claiming natural training history has attained naturally achievable results, the FFMI natural ceiling was established by the Kouri et al. analysis of drug-tested athletes and has been broadly replicated.

Honesty Scale: Solid (1) for FFMI as a more informative body composition metric than BMI.

What to do: Calculate your FFMI: divide your lean mass in kg (from DEXA) by your height in meters squared. For a 5'10" (1.78m) man with 80 kg lean mass: 80/3.17 = 25.2 FFMI, unusually high for natural training. For 70 kg lean mass: 70/3.17 = 22.1, excellent for a natural athlete over 40.

For the full picture, read The Strength/Grip Deep Dive

## Category 14: Testosterone / TRT