STACKD summary
EmergingMGF, PEG-MGF, IGF-1 LR3, and Follistatin-344: the muscle-signaling peptides
Real underlying biology in animals and cells, and almost nothing tested in the injectable forms actually sold.
Plain-language summary
These four compounds get grouped together because they all touch the same growth pathway that decides how much muscle tissue can build: IGF-1 signaling and its natural brake, myostatin. MGF and PEG-MGF are versions of a stretch-induced IGF-1 splice variant muscle makes locally after damage. IGF-1 LR3 is an engineered IGF-1 analog built to resist the body's normal binding-protein buffering. Follistatin-344 blocks myostatin and activin, the signals that put a ceiling on muscle growth. All four have genuinely interesting preclinical or lab-tool origins. None of them has a published human trial testing the actual injectable peptide product sold in research-chemical markets.
What was studied
Animal and cell-culture studies: the original stretch-induced MGF splice variant discovery in rabbit muscle, IGF-1 LR3 infusion studies in guinea pigs and diabetic rats, and myostatin-blocking studies across rodent, sheep, and dog models. The one exception is follistatin, where a systemically circulating gene-therapy version (delivered via AAV vector, not injected as protein) was tested in small human trials for Becker muscular dystrophy and inclusion body myositis.
Key takeaways
- MGF is not a separate hormone; it's an alternate way the body reads the IGF-1 gene after mechanical stretch or muscle damage, and human muscle biopsies confirm this splice variant does rise after resistance exercise, but that's the body's own gene expression, not evidence about the injected peptide.
- PEG-MGF's rationale is built entirely by combining two separate bodies of science, native MGF biology and pegylation as a general half-life-extension technique, without any dedicated study of the pegylated product itself.
- IGF-1 LR3 was engineered as a laboratory reagent to study IGF-1 receptor biology without binding-protein interference, not developed as a drug candidate; there is no published human trial of any kind.
- Follistatin's strongest human evidence comes from AAV gene-therapy trials that had patients' own muscle produce the protein locally, a fundamentally different delivery method than the injectable recombinant peptide sold as "Follistatin-344."
Limitations & what we don't know
- None of the four has a controlled human trial of the specific injectable research-chemical product being discussed and sold.
- Myostatin blockade's dramatic effects on muscle in animal models raise unanswered questions about proportional strengthening of tendons and connective tissue.
- IGF-axis peptides carry theoretical long-term concerns about unchecked cell proliferation and, for IGF-1 LR3 specifically, hypoglycemia risk given its insulin-like cross-reactivity.
- As unregulated research chemicals, sourcing, purity, and dosing consistency are not independently verified for any of the four.
Sources
Primary citations behind this summary. External links are provided for verification, read them yourself before drawing conclusions.