What it is
Whether you have low muscle mass for your age — sometimes combined with reduced strength or a slower walk into a single "sarcopenia" diagnosis. The evidence here is categorical only: you either meet the threshold or you don't. There is no dose curve to slide up as your muscle mass changes.
How it is modeled (not scored)
Technical notes
The curve is Liu 2017: community-dwelling older adults, 6 studies, 7,367 people. Sarcopenia (the composite consensus diagnosis — low muscle mass plus reduced function, not muscle mass alone) vs no sarcopenia, all-cause mortality HR 1.60 (1.24–2.06). Main source: Liu. Supporting: de Santana 2021 (the pure-muscle-mass counterpart, 9 studies, reports a standardized mean difference of -0.18 (-0.23 to -0.12) rather than a hazard ratio; no dose-response curve exists for muscle mass alone) / Knowles 2021 (UK Biobank, 356,590 people; found J-shaped associations between muscle mass and all-cause mortality, and concluded muscle-mass measurements were not superior to BMI for predicting mortality at the population level) / Zhang 2018 (nursing-home residents, a frailer population than the curve's community-dwelling cohort, HR 1.86 (1.42–2.45) — the association gets stronger, not weaker, in frailer people). Tian & Xu 2016 shows a related but distinct construct, sarcopenic obesity, sits lower at HR 1.24 (1.12–1.37) — construct-sensitive, not one settled number.
How to improve it
- Do resistance training 2–3x/week
- Eat enough protein, spread across meals
- Track strength and function, not just the scale
- Ask a clinician about a muscle-mass or sarcopenia screen if you are over 60