ALMI (appendicular lean mass index)

Appendicular lean mass index (ALMI) measures the muscle in your arms and legs, normalized for height. It is calculated by dividing the combined lean mass of all four limbs (in kilograms) by height squared (in meters squared), and a DEXA scan typically outputs the number directly. Typical values run roughly 8-10 kg/m² in men and 5-8 kg/m² in women, with wide variation by age and fitness level.

What ALMI measures, and why that matters

ALMI became the foundation of sarcopenia diagnosis when Baumgartner and colleagues defined low muscle mass as more than two standard deviations below the young-adult mean [1]. That framing has held up: subsequent work anchored cutpoints to clinically meaningful weakness, with the FNIH consortium setting thresholds at less than 19.75 kg total appendicular lean mass for men and less than 15.02 kg for women [2]. The current international consensus (EWGSOP2) still uses ALMI as a confirmatory tool, but it now positions low strength as the primary criterion, with low mass as supporting evidence [3]. The ordering matters.

ALMI is a cleaner muscle measure than fat-free mass index (FFMI), which bundles in trunk and organ mass alongside the contractile, fall-preventing tissue you care about. What ALMI does not capture is how well that muscle performs.

Mass vs. strength, the mortality distinction

A common framing treats a high ALMI as directly protective against early death. The primary literature tells a more precise story. In the Health ABC cohort, muscle strength predicted mortality while muscle mass did not, the two were measured in the same people, at the same time [4]. A 2019 analysis confirmed that neither ALMI nor ALM normalized to BMI was independently associated with mortality once physical performance measures were included; grip strength and gait speed were [5]. This converges with findings from the large PURE study, where grip strength outperformed systolic blood pressure as a mortality predictor [6].

The practical takeaway: ALMI is well-validated for defining and tracking muscle quantity over time. As a standalone mortality signal, it is weak-to-null once strength and physical performance enter the model. Strength is the more predictive endpoint.

How ALMI fits into a DEXA scan

A standard DEXA gives you four clinically useful numbers: ALMI (muscle quantity), bone mineral density (particularly relevant for women), visceral fat area, and body-fat percentage [7]. Tracking all four gives a more complete picture than any single value alone.

Peter Attia's clinical framing

Physician Peter Attia suggests targeting at or above the 75th percentile for your age and sex, treating that as a floor rather than a destination, specifically to preserve margin against the muscle loss that accumulates from the fifth decade onward [7]. He also frames ALMI as an integrator: the number reflects the training and protein intake that produced it, not a lever you pull directly [7]. That is a reasonable mechanistic argument, though it is worth keeping the primary evidence in view, the mass itself does not appear to drive mortality outcomes independently of what that muscle can do.

Where the evidence is contested

The original clinical literature built sarcopenia diagnosis almost entirely around low mass, with ALMI as the defining criterion [1]. EWGSOP2 shifted the framework by making low strength primary and treating low mass as confirmatory [3]. The two approaches agree on who has advanced sarcopenia but diverge on borderline cases, someone with low ALMI and preserved strength lands differently under each definition. Separately, studies differ on whether ALMI or ALM normalized to BMI performs better across body sizes; the FNIH work used absolute ALM thresholds [2], while other analyses favor the height-squared normalization. Neither debate changes the central finding that strength predicts mortality more robustly than mass does [4] [5], but it does affect how sarcopenia is counted and studied across populations.

References

1. Baumgartner 1998, Am J Epidemiol — original ALMI sarcopenia cutpoint · PubMed 9554417
2. Cawthon 2014 FNIH, J Gerontol A — weakness-anchored ALM cutpoints · PubMed 24737559
3. Cruz-Jentoft 2019 EWGSOP2, Age Ageing — strength-first sarcopenia consensus · PubMed 31081853
4. Newman 2006 Health ABC, J Gerontol A — strength (not mass) predicts mortality · PubMed 16456196
5. Sim 2019, JAMDA — ALMI not associated with mortality once function considered · PubMed 30527277
6. Leong et al. 2015, Lancet (PURE) — grip strength & mortality · PubMed 25982160
7. Attia ep.261 — Centenarian decathlon, Zone 2, VO2max (live AMA)