LBM vs muscle vs tape measurement

Muscle mass ≈ subset of LBM. Roughly 40–50% of LBM is skeletal muscle in healthy adults—the rest is water, bone, organs.

U.S. Navy tape formulas measure body fat directly from circumferences—often closer to “true” BF% for trained users who measure consistently.

Limitations

• Formulas estimate LBM from height and weight only—age is collected for context but does not change Boer/James/Hume math here
• Typical error vs DEXA is often ±3–5 percentage points of body fat; athletes and very lean individuals may see larger gaps
• LBM includes water, bone, and organs—not the same as skeletal muscle mass alone
• Not for pregnancy, edema, amputation, or clinical malnutrition without professional assessment
• Implied body fat % is derived from formula output, not measured with calipers or scans

References

• Boer P. et al., estimation of lean body mass — widely cited regression equations.
• NHLBI BMI categories — used for BMI display alongside LBM.