a These authors contributed equally to this work. Abstract Aged skeletal muscle has an attenuated and delayed ability to proliferate satellite cells in response to resistance exercise. The mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway is a focal point for cell growth, however, the effect of postexercise mTORC1 activation on human skeletal muscle satellite cell (SC) proliferation is unknown. To test the proliferative capacity of skeletal muscle SC in aging muscle to a

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... t mTORC1 activator (i.e., EAA; essential amino acids) we recruited older (~72y) men to conduct leg resistance exercise (8setsx10reps) without (ÀEAA; n = 8) and with (+EAA: n = 11) ingestion of 10 g of EAA 1 h postexercise. Muscle biopsies were taken before exercise (Pre) and 24 h postexercise (Post) for assessment of expression and fiber type-specific Pax7 + SC, Ki67 + Pax7 + SC and MyoD + SC. ÀEAA did not show an increase in Pax7 + satellite cells at Post(P > 0.82). Although statistical significance for an increase in Pax7 + SC at 24 h post-RE was not observed in +EAA versus ÀEAA, we observed trends for a treatment difference (P < 0.1). When examining the change from Pre to Post trends were demonstrated (#/myofiber: P = 0.076; and %/myonuclei: P = 0.065) for a greater increase in +EAA versus ÀEAA. Notably, we found an increase SC proliferation in +EAA, but not ÀEAA with increase in Ki67 + SC and MyoD + cells (P < 0.05). Ki67 + SC also exhibited a significant group difference Post (P < 0.010). Pax7 + SC in fast twitch myofibers did not change and were not different between groups (P > 0.10). CDK2, MEF2C, RB1 mRNA only increased in +EAA (P < 0.05). Acute muscle satellite cell proliferative capacity may be partially rescued with postexercise EAA ingestion in older men.