Does lean mass mean muscle?
Lean soft tissue includes muscle, organs and water. DEXA does not isolate all skeletal muscle from those other soft tissues. A change in a lean-tissue result is therefore not a direct measurement of muscle gained or lost.
Read the column heading carefully. ‘Lean + BMC’ includes bone mineral content, whereas a lean-soft-tissue measurement does not. Similar headings from different reports may represent different quantities.
Why might lean mass change between scans?
Preparation and analysis affect a comparison. ISCD identifies consistency in timing, food intake, physical activity, clothing and bladder state as important for repeatable body composition measurements. Follow the clinic’s preparation instructions.
Changes in a report can reflect a combination of tissue change, measurement variation and testing conditions. Bring both reports so the practitioner can check the method and context.
A worked example: arithmetic is not interpretation.
Imagine one report lists 51 kg of lean tissue and another lists 52 kg. The arithmetic difference is 1 kg. It does not establish that the person gained 1 kg of muscle.
Before drawing that conclusion, the practitioner needs to check comparability and measurement variation. These invented values illustrate a reading mistake; they are not expected results or targets.
What about arm and leg measurements?
Regional lean mass describes the tissue within the scanner’s defined region. Positioning and region boundaries matter when comparing one limb with another or comparing visits.
A left-to-right difference is not, on its own, a diagnosis of injury or weakness. Ask the practitioner to check the analysis and consider your symptoms, strength and history.
Reviewed guide: left and right regions ↗
ALMI is one part of the picture
The older-adult cut-points below concern muscle quantity and strength in a particular assessment framework. They are not athletic targets. Ask which measures are relevant to you and whether the report needs to be considered alongside an assessment of strength or function.
| Measure | Men | Women |
|---|---|---|
| Appendicular mass (ASM) | <20 kg | <15 kg |
| ASM / height² | <7.0 kg/m² | <5.5 kg/m² |
| Grip strength (not measured by DEXA) | <27 kg | <16 kg |
At your appointment
- Were these scans performed using comparable conditions?
- Is this change larger than the clinic’s measurement variation?
- How does it fit with my strength, symptoms and training record?
A sensible next step
Discuss the report with the practitioner who performed the scan. If you have unexplained weight loss or weakness, speak with your GP.
These suggestions are general information. Your own practitioner can review the full report and your history.