Sarcopenia in Ageing — Diagnostic Criteria, Investigation and Management

Sarcopenia in Ageing — Diagnostic Criteria, Investigation and Management A. 18 High-Yield Points Definition and Concept

Definition: Sarcopenia is the excessive loss of muscle mass that occurs in older people, usually defined as lean tissue more than two standard deviations below that of young adults.

Prevalence: 13–24% at ages 60–70, rising to about 50% over age 80.

Relationship to frailty: Sarcopenia is one of the five major causes of frailty and is the biological substrate of physical frailty — the two are two sides of the same "impaired" coin, and a combined entity, "physical frailty and sarcopenia," is emerging.

Sarcopenia is strongly correlated with disability. Most sarcopenic people also lose fat, but a subset stay fat while losing muscle — the "sarcopenic obese" or "fat frail" — and longitudinally these have the highest future disability and mortality.

Myosteatosis is a separate condition — fat infiltration into muscle, related to insulin resistance. Mitochondrial failure or high circulating triglycerides cause intramyocellular triglyceride accumulation, altering the insulin receptor substrate and GLUT transporter.

Final common mechanism: an imbalance in the everyday renewal cycle of muscle — either excess atrophy and apoptosis, or reduced hypertrophy and satellite cell production.

Best epidemiological predictors of muscle mass and strength: age, energy intake, physical activity, IGF-1, testosterone and cytokines.

Hormonal: Testosterone falls about 1% per year from age 30 in men, and rapidly between 20 and 40 in women. Testosterone diverts pluripotential stem cells away from the fat lineage into the muscle lineage, produces satellite cells (essential for muscle repair), stimulates muscle protein synthesis and inhibits the ubiquitin– proteasome pathway.

Growth factors: Myostatin is the negative regulator, acting via activin IIb receptors; a soluble activin IIb receptor scavenges activin and produces muscle and bone hypertrophy in rodents, monkeys and humans. Double myostatin deletion produces the "mighty mouse," and marked hypertrophy in cattle, whippets and one human. IGF-1 and mechanogrowth factor (MGF) rise with resistance exercise in young but not elderly subjects.

Neural: Motor unit firing rate falls significantly after age 80. Ciliary neurotrophic factor (CNTF) declines with age in parallel with strength. C-agrin and neurofilament light chain are raised in a subset of sarcopenic people.

Inflammatory, vascular and developmental: Excess TNF-alpha and IL-6 cause loss of muscle strength; high CRP and IL-6 correlate with reduced handgrip strength. Raised homocysteine and peripheral vascular disease impair muscle blood flow. Hypovitaminosis D is associated with decreased strength and falls. In the Hertfordshire cohort, grip strength correlated with birth weight — sarcopenia may originate at birth. ACE I/I carriers generate more power with exercise than D allele carriers.

Signalling pathway: anabolic limb — GH/testosterone/creatine → IGF-1/MGF → PI3K → AKT → mTOR → S6K1 → hypertrophy; catabolic limb — cytokines → TNFR1 → IKK → NF-kappaB, and glucocorticoids/diabetes → FOXO → Atrogin-1 (MAFbx) and MuRF1 → ubiquitin–proteasome → protein degradation → atrophy; myostatin → SMAD3 suppresses MyoD, opposed by follistatin.

Best measure of muscle mass: appendicular skeletal mass measured by DEXA, divided by height in metres squared. Alternatives: MRI, CT, or bioelectrical impedance. DEXA and MRI measures are highly correlated, and ultrasound is proving to be an excellent measure.

Imaging refinement: MRI with specific protocols is superior to DXA, particularly for visceral tissues, and can additionally measure muscle volume, muscle fat infiltration and ectopic fat. BIA is accessible even in primary care but relies on an approximation between total body weight, lean tissue and fat — reasonable for arms and legs, less precise for visceral regions.

Circulating biomarkers: - P3NP (procollagen type III N-terminal peptide) — related to muscle mass and strength, stronger in women. - D3-creatine (methyl-d3) dilution — urine D3-creatinine enrichment correlates highly with MRI total muscle mass and may be superior to DXA. - C-terminal agrin fragment (CAF) — a neuromuscular junction breakdown product; associated with DXA muscle mass, grip strength and gait velocity. - Myostatin, follistatin, GDF-11 — inconsistent; the myostatin–muscle mass relationship was confirmed only in men in the I-Lan study.

Core treatment: Resistance exercise plus adequate protein (1 g/kg/day) — the explicit treatment for sarcopenia in the FRAIL management algorithm; plus aerobic and balance exercise. Creatine with exercise may improve muscle performance.

Pharmacological options: Testosterone replacement increases muscle mass even in non-hypogonadal males; pharmacological or replacement doses in hypogonadal men increase muscle strength and power, with demonstrated functional improvement. Selective androgen receptor modulators — steroidal (nandrolone, oxymetholone, oxandrolone) and non-steroidal (2-quinoline, coumarin, phthalimide, bicalutamide, acetothiolutamide) — remain investigational.

What NOT to use, and what else to do: Growth hormone is not recommended — it produced no positive effect on muscle strength, VO2max or functional capacity, did not add to resistance training, and men with the highest GH levels had the highest mortality. Vitamin D — regular sun exposure 15–30 minutes a day without sunblock, or 800–1000 IU/day; 25-OH-vitamin D should be above 30 ng/mL. Treat the anorexia of ageing using the MEALS-ON-WHEELS mnemonic.

GLIS — the first globally endorsed conceptual definition (2024). The Global Leadership Initiative in Sarcopenia defined sarcopenia as a generalised skeletal muscle condition that is potentially reversible, applying consistently across conditions, care settings and both clinical and research contexts. Its core components are muscle mass, muscle strength and muscle-specific strength (strength divided by size), while impaired physical performance is a consequence, not a diagnostic component. This is the single biggest conceptual change since the textbook.

GLIS outcomes consensus (2025). From an individual patient data meta-analysis of 32 databases and 5,116 participants using the SarQoL instrument, people with sarcopenia have significantly reduced quality of life (mean difference −12.32), with the largest difference using AWGS criteria (−17.65).

Regional guidelines have proliferated. Australia/New Zealand consensus (2023), Singapore clinical practice guidelines (2022), Chinese guidelines (2025), and an AWGS update. DXA remains a standard but has limitations in reflecting true muscle quality and predicting outcomes; deuterium-labelled creatine dilution shows promise, and myokine biomarkers (IL-6, IGF-1, irisin, myostatin, gelsolin) may improve diagnostic precision.

Exercise — now a formal prescription. The ICFSR global consensus (2025) states that structured exercise prescriptions should be customised and monitored like any other medical treatment, with a multifaceted regimen of aerobic, resistance, balance and flexibility training. Combined resistance–aerobic regimens at 2–3 sessions per week improve muscle strength by 20–35%.

Nutrition — the numbers have firmed up. Optimised protein intake of 1.0–1.5 g/kg/day with leucine or vitamin D enhances muscle synthesis and functional capacity. To overcome the anabolic resistance of ageing muscle, 25–30 g of high-quality protein and 2.8–3 g of leucine per meal, at least twice daily, is recommended; requirements rise to 1.2– 1.5 g/kg/day in inflammatory disease. HMB 3 g daily helps preserve muscle during illness, immobility or post-surgical recovery — the evidence is stronger for preventing loss than for building muscle.

Pharmacotherapy — still investigational. SARMs and myostatin inhibitors such as bimagrumab increase lean mass by 3–5% in phase II studies; a single dose of the ActRIIB antibody bimagrumab produced a 6–8% increase in muscle mass within a month with a simultaneous reduction in fat mass. GDF-15-neutralising antibodies are emerging as anti-catabolic agents. No agent is approved for sarcopenia anywhere as of 2026 — exercise plus protein remains the only proven therapy.

Vitamin D — nuance added. Recent trials show active vitamin D (0.75 microgram/day) can improve muscle strength and reduce fall risk in sarcopenic individuals, but benefits are largely confined to those who are deficient.

Indian relevance. Grip strength was the most discriminant frailty and sarcopenia component in Indian men (79.1%) in LASI, and AWGS cut-offs, not EWGSOP2, should be applied to Indian patients. BIA is the practical mass-measurement modality in most Indian centres given limited DXA access — AWGS explicitly provides a BIA cut-off for this reason.