Appendicular-to-trunk lean mass ratio resolves the height-based normalization paradox in low muscle mass and metabolic syndrome: A population-based cross-sectional study.
ALM/TLM (appendicular-to-trunk lean mass ratio) resolves the height-based normalization paradox by correlating negatively with adiposity and showing consistently positive associations between low muscle mass and metabolic syndrome, whereas ASMI (ALM/height²) correlates positively with adiposity and paradoxically shows an inverse association between low muscle mass and metabolic syndrome.
Key Findings
Results
ASMI (ALM/height²) correlated positively with fat mass index in both sexes, whereas ALM/TLM correlated negatively with fat mass index.
ASMI–FMI correlations: men r=+0.288, women r=+0.358, both p<0.001
ALM/TLM–FMI correlations: men r=-0.199, women r=-0.243, both p<0.001
These opposing correlations suggest ASMI may partly reflect body size and adiposity rather than relative muscle depletion alone
Body composition was measured by dual-energy X-ray absorptiometry (DXA) in adults aged ≥65 years (n=3,176; 1,373 men, 1,803 women)
Results
ASMI-defined Class I low muscle mass showed a paradoxical inverse association with metabolic syndrome in both men and women.
Men: OR 0.496, 95% CI 0.388–0.636
Women: OR 0.475, 95% CI 0.328–0.686
The authors explicitly state this inverse association 'should not be interpreted as protective'
The paradox is attributed to ASMI's positive correlation with adiposity, meaning higher-adiposity individuals tend to have higher ASMI scores
Results
ALM/TLM Class II low muscle mass showed consistently positive associations with metabolic syndrome in both men and women.
Men: OR 2.779, 95% CI 2.074–3.722, p<0.001
Women: OR 2.701, 95% CI 1.680–4.340, p<0.001
These positive associations were consistent across adiposity strata
Metabolic syndrome was defined by NCEP-ATP III criteria with population-specific waist cut-offs
Results
The inverse association between ALM/TLM and HOMA-IR (insulin resistance) persisted after adjustment for fat mass index.
Men: β=-0.131, p<0.001 after FMI adjustment
Women: β=-0.065, p=0.007 after FMI adjustment
Survey-weighted regression models were additionally adjusted for age, smoking, alcohol, and physical activity
This persistence after FMI adjustment suggests ALM/TLM captures muscle-related metabolic information independent of adiposity
Methods
Sex-specific cut-offs for ALM/TLM were derived from a healthy young reference population at 1 SD and 2 SD below the young-adult mean.
Reference group comprised 3,727 adults aged 20–39 years from the Korea National Health and Nutrition Examination Survey 2008–2010
Class I cut-offs were defined at 1 SD below the young-adult mean; Class II at 2 SD below
Both ALM and TLM were measured with bone mineral content excluded
The same SD-based derivation approach was applied to ASMI for comparison
Methods
The study used a large population-based sample of Korean older adults from the Korea National Health and Nutrition Examination Survey 2008–2010.
Total analytic sample: 3,176 adults aged ≥65 years (1,373 men; 1,803 women)
Cross-sectional design with survey-weighted analyses to account for the complex sampling strategy
Covariates in regression models included age, smoking, alcohol consumption, and physical activity
The study population was entirely Korean, which may limit generalizability to other ethnic groups
What This Means
This research suggests that a commonly used method for diagnosing low muscle mass in older adults — dividing appendicular (arms and legs) lean mass by height squared (ASMI) — has a built-in flaw: it tends to give higher scores to people who are fatter, because heavier people generally have more muscle mass in absolute terms. As a result, when researchers used ASMI to identify low muscle mass, people flagged as having low muscle surprisingly appeared to have lower rates of metabolic syndrome (a cluster of conditions including high blood pressure, high blood sugar, and abnormal cholesterol). This counterintuitive finding — where 'low muscle' appears protective — is what the authors call the 'height-based normalization paradox.'
The study tested an alternative measurement called ALM/TLM, which compares arm and leg lean mass to trunk (torso) lean mass, rather than to height. Unlike ASMI, ALM/TLM was negatively correlated with body fat, meaning fatter individuals scored lower on this ratio. When using ALM/TLM to define low muscle mass, the paradox disappeared: people with low ALM/TLM consistently had higher rates of metabolic syndrome, with roughly 2.7 to 2.8 times the odds compared to those with normal ratios. This pattern held true across different levels of body fatness and in both men and women.
This research suggests that how muscle mass is normalized — the denominator used in the calculation — profoundly affects whether the measure actually reflects muscle depletion or is partly capturing body size and fat. The ALM/TLM ratio appears to better isolate relative muscle loss from adiposity-related influences, and may be worth further investigation as a tool for identifying older adults at metabolic risk. The authors caution, however, that the clinical validity of ALM/TLM remains unestablished and further research is needed before it can be recommended for clinical use.
Check Your Own Numbers
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Lim J, Yu S, Park J, Moon S, Lee C, Hong S. (2026). Appendicular-to-trunk lean mass ratio resolves the height-based normalization paradox in low muscle mass and metabolic syndrome: A population-based cross-sectional study.. PloS one. https://doi.org/10.1371/journal.pone.0357017