Make the next check-in useful
Upload a photo to LeanLens, get a confidence-aware read, and use the article framework to choose one practical next step.
Illustrative body-composition report: what each line means
| Report line | Example | Evidence type and limit |
|---|---|---|
| Body weight | 70 kg entered from a scale | Entered measurement; scale conditions can change the reading. |
| Body-fat percentage | 20% entered estimate | Estimate, not a direct measurement of tissue compartments. |
| Fat mass | 14 kg = 70 kg × 20% | Calculated from the entered weight and estimated percentage; inherits both inputs’ uncertainty. |
| Fat-free mass | 56 kg = 70 kg − 14 kg | Derived remainder that includes more than skeletal muscle. |
| FFMI | Fat-free mass divided by height squared | A derived ratio; it inherits uncertainty from body-fat estimation and height. |
Read the compartment label
A useful conceptual map is body mass → fat mass + fat-free mass. Within fat-free mass are skeletal muscle, organs, bone, water and other non-fat components. These categories overlap chemically: water exists within muscle and organs, so do not add them together as separate scale compartments.
DEXA reports lean soft tissue separately from bone mineral. A consumer app may use “lean mass” as shorthand for weight minus estimated fat. Check the method before comparing values with the same label.
A numerical example of the difference
At 70 kg with an entered fat estimate of 20%, calculated fat mass is 14 kg and fat-free mass is 56 kg. It would be incorrect to report 56 kg of skeletal muscle. The subtraction has not isolated a specific tissue.
If estimated fat-free mass changes between check-ins, examine the body-fat estimate, weight, preparation and device first. Short-term water or glycogen differences can affect appearance and some measurement outputs without showing newly built muscle.
Make the next check-in useful
Upload a photo to LeanLens, get a confidence-aware read, and use the article framework to choose one practical next step.
How this affects FFMI and photo scores
FFMI uses fat-free mass, not a direct skeletal-muscle measurement. The FFMI calculator therefore inherits the uncertainty of the input percentage.
LeanLens muscle-balance feedback interprets visible development and proportions. A 0–10 muscle score is not a kilogram value. Use photos and training records for context and appropriate professional testing when tissue measurement matters.
Limits and safety
LeanLens content is informational fitness guidance, not medical advice, diagnosis, or treatment. Photo-based analysis should be used for trend direction and practical next steps, not clinical decisions.
FAQ
Is lean mass the same as muscle mass?
No. Skeletal muscle is one component of broader non-fat tissue. Exact terminology depends on the measurement method.
Does losing lean mass mean I lost the same amount of muscle?
No. A lean-mass estimate can include changes in water and other components; it does not isolate skeletal muscle.