Myostatin: What It Is and What Influences It
Myostatin is a protein that acts as a brake on muscle growth. Its discovery through extraordinarily muscular cattle and mice made it a favourite topic in bodybuilding forums. Our editorial team explains what myostatin does, what genuinely influences it and why experimental inhibitors are not a shortcut to muscle.
What myostatin is
Myostatin, also known as growth differentiation factor 8 (GDF-8), belongs to the transforming growth factor beta (TGF-β) family of signalling proteins. It is produced mainly by skeletal muscle cells and released into the circulation, where it acts on muscle tissue.
Its main role is to limit muscle mass. Myostatin binds to activin type II receptors on muscle cells, triggering a signalling cascade through proteins called SMAD2 and SMAD3. This inhibits muscle protein synthesis pathways, including Akt and mTOR, and reduces the proliferation of satellite cells.
From an evolutionary perspective, limiting muscle mass makes sense. Muscle is metabolically expensive tissue, and an organism that built muscle without restraint would need far more energy to survive, particularly when food was scarce.
Myostatin was first described in 1997 by Se-Jin Lee and Alexandra McPherron, who showed that mice lacking the gene developed roughly twice the normal muscle mass. This finding sparked decades of research into muscle wasting diseases.
Natural mutations in animals and humans
Some cattle breeds, such as Belgian Blue and Piedmontese, carry natural mutations in the myostatin gene. They show the so-called double-muscling phenotype, with a striking increase in muscle mass and reduced fat. Whippet dogs with one copy of a mutation are faster racers; those with two copies are heavily muscled 'bully whippets'.
In 2004, a report in the New England Journal of Medicine described a German child with mutations in both copies of the myostatin gene who had exceptional muscle development from birth. The case confirmed that myostatin regulates muscle mass in humans as well.
Such mutations are very rare in humans. Common genetic variants in the myostatin gene among the general population have only small, inconsistent associations with muscle size or strength, and genetic testing for them has no practical value in training.
Animal breeding also shows downsides. Double-muscled cattle can have calving difficulties and differences in tendon properties, illustrating that extreme muscle growth may come with physiological trade-offs.
What influences myostatin naturally
Resistance training is the most reliable natural influence. Studies have found that a session of heavy lifting reduces myostatin gene expression in the trained muscle for hours afterwards. This reduction is one of many signals that help muscle adapt and grow.
Disuse has the opposite effect. Bed rest, limb immobilisation and spaceflight are associated with increased myostatin activity, which contributes to rapid muscle loss. This is one reason why early mobilisation after illness or surgery matters.
Chronic conditions such as heart failure, chronic kidney disease, cancer cachexia and HIV-associated wasting are linked to elevated myostatin. Ageing may also involve changes in myostatin signalling, although findings on circulating levels in older adults are inconsistent.
| Factor | Effect on myostatin | Practical relevance |
|---|---|---|
| Resistance exercise | Decreases expression locally | High: core of muscle building |
| Immobilisation | Increases activity | Keep moving after injury where safe |
| Chronic disease | Often elevated | Treat the underlying condition |
| Adequate protein and energy | Indirect support for muscle | High |
| 'Myostatin blocker' supplements | Weak or no human evidence | Low |
Supplements and experimental drugs
Several supplements claim to inhibit myostatin, including products based on follistatin from egg yolk, epicatechin from cocoa and certain algae extracts. Evidence in humans is limited to small studies, often with surrogate markers, and none has shown convincing increases in muscle mass in healthy adults.
Pharmaceutical companies have developed antibodies against myostatin or its receptors, such as bimagrumab, and tested them in conditions like sarcopenia, muscular dystrophy and obesity. Some showed increases in lean mass, but improvements in physical function were often modest, and several programmes were discontinued.
These experimental drugs are not licensed medicines in the UK for muscle building. Products sold online claiming to contain them are unregulated, of unknown composition and may be counterfeit, carrying risks of infection, immune reactions and contamination.
- Myostatin-inhibiting supplements: weak evidence, high marketing.
- Experimental antibodies: research settings only, mixed results.
- Gene-based approaches: experimental, with unknown long-term safety.
Anti-doping and safety considerations
The WADA Prohibited List includes myostatin inhibitors among the substances banned at all times, alongside agents that modify the activin receptor pathway. Gene doping, meaning the use of nucleic acids or gene editing to enhance performance, is also prohibited.
UK Anti-Doping enforces these rules under the principle of strict liability. Athletes are responsible for any prohibited substance in their bodies, regardless of intent, and online products marketed as myostatin blockers may contain undeclared prohibited ingredients.
From a safety perspective, the activin pathway is involved in many tissues beyond muscle, including blood vessels, bones and reproductive organs. Some clinical trials of activin receptor drugs reported side effects such as nosebleeds and telangiectasias, small dilated blood vessels.
The safest and most effective way to work with myostatin biology remains consistent resistance training, adequate protein and energy intake, sufficient sleep and avoiding long periods of inactivity.
Editorial conclusions
Myostatin is a natural brake on muscle growth that acts through the activin receptor and SMAD signalling pathway.
Resistance training reduces its expression, while inactivity and chronic disease increase it; supplements claiming to block it have little supporting evidence.
Experimental inhibitors remain research tools, are banned in sport and carry unknown risks when obtained outside clinical trials.
Our editorial team suggests reading next about how mTOR controls muscle growth, sarcopenia prevention and the science of muscle hypertrophy.
References
- McPherron AC, Lawler AM, Lee SJ. Regulation of skeletal muscle mass in mice by a new TGF-beta superfamily member. Nature. 1997;387(6628):83–90.
- Schuelke M, Wagner KR, Stolz LE, et al. Myostatin mutation associated with gross muscle hypertrophy in a child. N Engl J Med. 2004;350(26):2682–2688.
- Mosher DS, Quignon P, Bustamante CD, et al. A mutation in the myostatin gene increases muscle mass and enhances racing performance in heterozygote dogs. PLoS Genet. 2007;3(5):e79.
- Rooks D, Praestgaard J, Hariry S, et al. Treatment of sarcopenia with bimagrumab: results from a phase II, randomized, controlled, proof-of-concept study. J Am Geriatr Soc. 2017;65(9):1988–1995.
- Lee SJ. Regulation of muscle mass by myostatin. Annu Rev Cell Dev Biol. 2004;20:61–86.
- Kollias HD, McDermott JC. Transforming growth factor-beta and myostatin signaling in skeletal muscle. J Appl Physiol. 2008;104(3):579–587.
