MGF

The MGF evidence base cited here is 7 sources — 1 clinical, 5 preclinical, 1 review. Its strongest evidence is human — a clinical study, most recently 2009 ("Expression of IGF-1 isoforms after exercise-induced muscle damage in hum…"). Regulatory status: Not FDA-approved.

• MGF is generated by alternative splicing of the IGF-1 gene in mechanically stressed skeletal muscle; the splice variant produces an E-domain peptide that acts transiently and locally to activate muscle satellite cells, initiating a proliferative burst before longer-lived IGF-1Ea drives terminal differentiation.
• Exercise-induced muscle damage in humans produces a rapid, transient upregulation of MGF mRNA within hours of eccentric contraction, with the synthetic MGF E peptide activating signaling pathways independent of the classic IGF-1 receptor, suggesting a distinct paracrine mechanism.
• Age-related failure to upregulate MGF after mechanical overload — demonstrated in older rat muscle — is proposed as a key driver of sarcopenia; older muscles showed markedly lower MGF expression and failed to upregulate IGF-1 receptor or MyoD following the same stimulus that robustly activated young muscle.

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