Lean Mass Index (LMI)
Lean Mass Index (LMI) is total lean mass divided by height squared (kg/m²). It normalises lean mass for body size the same way BMI normalises body weight, allowing fair comparison across people of different heights. Data are from Kelly et al. 2009, a cross-sectional analysis of DXA body composition scans from 15,258 US adults in NHANES 1999 to 2004. Percentiles were derived using LMS curve fitting applied to the White (non-Hispanic) reference population. Kelly et al. also provide curves for Black and Mexican American adults; values differ, with Black adults showing higher lean mass at equivalent ages. These norms are most applicable to White Western adults and may not represent other ethnic groups.
Data source: Kelly et al. (NHANES DXA) About this study
Lean Mass Index (LMI) Norms by Age and Sex (kg/m²)
| Age | Sex | Percentile | ||||
|---|---|---|---|---|---|---|
| 5th | 25th | 50th | 75th | 95th | ||
| 20-24 | Male | 15.63 | 17.44 | 18.98 | 20.84 | 24.32 |
| Female | 12.96 | 14.37 | 15.6 | 17.11 | 20.06 | |
| 25-29 | Male | 15.9 | 17.75 | 19.31 | 21.17 | 24.61 |
| Female | 13.08 | 14.55 | 15.83 | 17.41 | 20.52 | |
| 30-34 | Male | 16.14 | 18.02 | 19.6 | 21.47 | 24.86 |
| Female | 13.18 | 14.7 | 16.03 | 17.68 | 20.92 | |
| 35-39 | Male | 16.33 | 18.25 | 19.85 | 21.72 | 25.07 |
| Female | 13.25 | 14.82 | 16.19 | 17.9 | 21.29 | |
| 40-44 | Male | 16.48 | 18.44 | 20.04 | 21.9 | 25.18 |
| Female | 13.29 | 14.89 | 16.3 | 18.06 | 21.55 | |
| 45-49 | Male | 16.57 | 18.54 | 20.15 | 22 | 25.2 |
| Female | 13.31 | 14.93 | 16.36 | 18.14 | 21.67 | |
| 50-54 | Male | 16.57 | 18.55 | 20.15 | 21.97 | 25.09 |
| Female | 13.28 | 14.92 | 16.35 | 18.14 | 21.66 | |
| 55-59 | Male | 16.5 | 18.48 | 20.07 | 21.86 | 24.88 |
| Female | 13.23 | 14.87 | 16.3 | 18.08 | 21.56 | |
| 60-64 | Male | 16.39 | 18.35 | 19.91 | 21.65 | 24.54 |
| Female | 13.19 | 14.81 | 16.21 | 17.94 | 21.31 | |
| 65-69 | Male | 16.22 | 18.16 | 19.67 | 21.34 | 24.08 |
| Female | 13.12 | 14.71 | 16.08 | 17.76 | 20.99 | |
| 70-74 | Male | 16.02 | 17.9 | 19.36 | 20.95 | 23.52 |
| Female | 13.05 | 14.59 | 15.92 | 17.53 | 20.59 | |
| 75-79 | Male | 15.77 | 17.59 | 18.98 | 20.49 | 22.89 |
| Female | 12.95 | 14.45 | 15.73 | 17.27 | 20.14 | |
| 80-84 | Male | 15.51 | 17.26 | 18.58 | 20 | 22.22 |
| Female | 12.85 | 14.3 | 15.53 | 17 | 19.7 | |
| 85+ | Male | 15.22 | 16.9 | 18.16 | 19.49 | 21.56 |
| Female | 12.75 | 14.15 | 15.32 | 16.71 | 19.25 | |
What to expect by age group
Among adults aged 30 to 34, the middle 50% measure 18.0 to 21.5 kg/m² for men and 14.7 to 17.7 kg/m² for women. LMI rises slightly into the 40s to 50s, then declines steadily as lean mass is lost with age; men carry around 3 to 4 kg/m² more lean mass relative to height than women. Scores below 18.0 kg/m² (men) or 14.7 kg/m² (women) are typically below average for this age group; scores above 21.5 kg/m² (men) or 17.7 kg/m² (women) are above average.
| Age | Males | Females |
|---|---|---|
| 20-24 | 17.44 to 20.84 | 14.37 to 17.11 |
| 25-29 | 17.75 to 21.17 | 14.55 to 17.41 |
| 30-34 | 18.02 to 21.47 | 14.7 to 17.68 |
| 35-39 | 18.25 to 21.72 | 14.82 to 17.9 |
| 40-44 | 18.44 to 21.9 | 14.89 to 18.06 |
| 45-49 | 18.54 to 22 | 14.93 to 18.14 |
| 50-54 | 18.55 to 21.97 | 14.92 to 18.14 |
| 55-59 | 18.48 to 21.86 | 14.87 to 18.08 |
| 60-64 | 18.35 to 21.65 | 14.81 to 17.94 |
| 65-69 | 18.16 to 21.34 | 14.71 to 17.76 |
| 70-74 | 17.9 to 20.95 | 14.59 to 17.53 |
| 75-79 | 17.59 to 20.49 | 14.45 to 17.27 |
| 80-84 | 17.26 to 20 | 14.3 to 17 |
| 85+ | 16.9 to 19.49 | 14.15 to 16.71 |
Detailed Breakdowns
Select an age group and sex below for detailed percentile charts, tables, and ratings.
Frequently Asked Questions
What is Lean Mass Index?
Lean Mass Index (LMI) is total lean body mass divided by height squared (kg/m²). It is analogous to BMI but measures the lean (non-fat) component of body mass. A higher LMI indicates more muscle and lean tissue relative to height.
How is lean mass measured?
The reference data use dual-energy X-ray absorptiometry (DXA), which is considered the gold standard for body composition measurement. DXA distinguishes fat mass, lean mass, and bone mineral content with high precision.
What counts as lean mass?
Lean mass includes muscle, organs, bone-free water, and connective tissue, everything except fat and bone mineral. It is dominated by skeletal muscle but also includes organ mass.
How does LMI differ from Appendicular Lean Mass Index (ALMI)?
LMI uses total body lean mass; ALMI uses only the arms and legs (appendicular lean mass). ALMI is more commonly used in clinical settings for sarcopenia screening because limb muscle is more sensitive to age-related muscle loss than trunk muscle.
Why do these norms use the White reference population?
Kelly et al. 2009 provides separate LMS curves for White, Black, and Mexican American adults. This site uses the White reference as the primary comparator for a predominantly US/European audience. Black Americans tend to have higher lean mass at the same age, while Mexican Americans fall between the two.
Are these norms representative of non-US populations?
These norms use the White (non-Hispanic) reference curves from NHANES. Kelly et al. 2009 also provides curves for Black and Mexican American adults, Black adults tend to have higher lean mass at equivalent ages. European populations are broadly comparable to the White NHANES reference, though some variation exists.