Myostatin

Where it comes from

Made in

Skeletal muscle, and in smaller amounts heart and fat

Sent out by

Circulates bound to its propeptide and follistatin; freed by proteases (BMP-1/tolloid) in muscle

Acts on

• Muscle satellite cells and fibres
• Fat tissue
• Bone

What it does

• Limits muscle fibre size and number from before birth
• Its absence gives double-muscled cattle, whippets, and one famously strong child
• Rises with inactivity, illness and age

In medicine

• Antibodies against myostatin (domagrozumab) or its receptor (bimagrumab) failed to improve function in Duchenne dystrophy and inclusion body myositis
• Apitegromab, an antibody against the latent form, improved motor function in spinal muscular atrophy in phase 3 by 1.8 points on a 66-point motor scale, with the higher dose alone falling short of significance ¹
• It was approved in the US in September 2026 for people aged two and over already on an SMN2-targeted treatment, the first myostatin medicine to reach approval; the label warns that it may raise the risk of fracture ²

Beyond the body’s own use

• Myostatin and activin-receptor blockers are in trials paired with GLP-1 medicines to keep muscle during weight loss. In a phase 2 trial of 507 adults, bimagrumab with semaglutide took off 17.8 kg over 48 weeks against 14.2 kg for semaglutide alone; whether the muscle is spared is the point still to be proved, and no such use is approved ³
• Follistatin and “myostatin inhibitor” supplements have no evidence in people, and the gene-doping version of the idea has none either
• Myostatin inhibitors, follistatin among them, are prohibited in sport at all times, in and out of competition ⁴