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FFMI Norms: Why 25 Is Not a Natural Limit

Body Composition3 min readKouri et al. (1995); Harty et al. (2019)

Fat-Free Mass Index scales lean mass to height. The famous 25 'natural limit' does not survive the paper it came from.

Key points
  • The 25 figure comes from a 1995 study of 157 male lifters, 74 of them drug-free.
  • Twenty pre-steroid Mr America winners in the same paper averaged 25.4.
  • Read 25 as roughly where drug-free lifters start becoming uncommon, not as a wall.
  • No equivalent study exists for women; one study of female collegiate athletes found a mean of 18.8.

Where 25 comes from

Fat-Free Mass Index scales how much lean mass you carry to your height, so it compares across body sizes the way a raw lean mass figure cannot. The number most people have heard is 25, and it comes from a 1995 study of 157 male lifters, 83 of whom used anabolic steroids and 74 of whom did not. The non-users stopped at 25.0; the users went well past it and some cleared 30. It has been read as a natural limit ever since.

What the paper actually shows

That reading does not survive the paper itself. The same study estimated FFMI for twenty Mr America winners from 1939 to 1959, before steroids reached the sport, and that group averaged 25.4: thirteen of the twenty sat above 25 and the highest was 28.0. The famous figure is below the mean of the drug-free group it was checked against. The non-user sample was also 74 men who needed only two years of training to qualify, which is not a group near anyone's ceiling. Read 25 as roughly where drug-free lifters start becoming uncommon, not as a wall.

Women

For women the honest answer is a different shape. FFMI is the same calculation, and reference figures exist: women within the normal BMI range sit around 14.6 to 16.8, and a study of 372 female collegiate athletes found a mean of 18.8 with the 97.5th percentile at 23.9. What does not exist is the female version of that 1995 study (nobody has contrasted drug-free women against known users), so there is no equivalent number, and a source quoting one has invented it. A figure of 21 to 22 attributed to that paper circulates widely; it measured 157 men and says nothing about women at all.

Different instruments

One caution that applies to every figure above. They come from different instruments: bioelectrical impedance, DXA, skinfold calipers, and in the historical case estimates made from photographs. Those do not return the same number for the same person, so read each against its own group rather than as points on one scale.

How Kriterion uses this

Kriterion's FFMI calculator gives your raw and height-normalised figures, and sets them beside the published groups they came from rather than beside a ceiling nobody measured.

References

  1. Kouri EM, Pope HG, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine, 1995;5(4):223-228.
  2. Harty PS, Zabriskie HA, Stecker RA, Currier BS, Moon JM, Jagim AR, Kerksick CM. Upper and lower thresholds of fat-free mass index in a large cohort of female collegiate athletes. Journal of Sports Sciences, 2019;37(20).
  3. Schutz Y, Kyle UUG, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y. International Journal of Obesity, 2002;26(7):953-960.
  4. VanItallie TB, Yang MU, Heymsfield SB, Funk RC, Boileau RA. Height-normalized indices of the body's fat-free mass and fat mass. The American Journal of Clinical Nutrition, 1990.

Last reviewed 28 Sep 2026 · Next review due Sep 2029

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