Regular resistance exercise elevates insulin-like growth factor-1 (IGF-1) through two distinct production routes — hepatic secretion via the GH-IGF-1 endocrine axis and local muscle synthesis through mechano-sensitive mechano growth factor (MGF) induction. This circulating IGF-1 reaches the brain via three documented pathways: LRP-1-mediated transcytosis across the blood-brain barrier, LRP-2 transport across the blood-cerebrospinal fluid barrier at the choroid plexus, and passive diffusion through circumventricular organs. Once inside the CNS, IGF-1 reactivates Akt to suppress GSK-3β-driven tau hyperphosphorylation while simultaneously dampening pathological MAPK/ERK overactivation, collectively reducing amyloid-beta generation, neuroinflammation, and neuronal apoptosis.
This is a mechanistically sophisticated synthesis that moves beyond the familiar "exercise is good for the brain" narrative into actionable pathway-level specificity. The PI3K/Akt–MAPK/ERK cross-inhibitory balance framing is particularly valuable: it explains why either pathway in isolation produces incomplete benefit, and why timing matters. The authors' candid "double-edged sword" caveat — that excessive or mistimed IGF-1 activation may worsen late-stage Alzheimer's pathology — is an underappreciated clinical reality often missing from exercise-enthusiasm literature. The primary limitation is that this is a review, not original trial data; the mechanistic chain remains partly inferred from animal models and cell studies. Still, the integrated framework offers a credible rationale for designing stage-specific resistance exercise prescriptions, a practical and low-risk intervention warranting urgent randomized trial investigation in early-to-mild Alzheimer's populations.