An infused antibody blocking the body's main brake on muscle growth, binding only its inactive stored form. It added movement capacity in a childhood nerve-and-muscle disease and protected lean tissue during weight loss on appetite-lowering medicines, with no gain in grip strength. Side effects were mild. Experimental everywhere, banned in sport, reachable only through trials. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Lean body mass by scan | Stable or rising; loss under 15% of any concurrent weight loss | The primary demonstrated effect |
| Grip force and sit-to-stand repetitions | Held or improved versus own baseline | Distinguishes capability from scan numbers |
| Serum latent myostatin | No established value; rise from own baseline to a plateau by week 16 | Confirms the drug is engaging its target |
| Creatine kinase | 30–200 U/L, and no rise above 5× the upper limit | Flags muscle stress; drives protocol stopping rules |
| Anti-drug antibodies | Negative; transient titre ≤10 acceptable | Predicts loss of effect and hypersensitivity |
| Alanine and aspartate aminotransferase | 10–30 U/L, below conventional cut-offs | Baseline liver safety; unchanged on drug |
| Glycated haemoglobin | 4.8–5.4% | Detects metabolic gain from preserved muscle |
| High-sensitivity C-reactive protein | Below 1.0 mg/L | Background inflammation drives muscle breakdown and can mask benefit |
| Estimated glomerular filtration rate | Above 90 mL/min/1.73 m² | Kidney screening; kidney disease excluded people from trials |
| 25-hydroxyvitamin D | 40–60 ng/mL | Low status impairs muscle function and confounds attribution |
Cadence: Safety chemistry before each infusion for three months, then every second infusion; body-composition scanning at baseline, week 24, then annually; motor or strength testing at 6 and 12 months, then yearly; anti-drug antibodies at baseline, month 3 and month 12.