CREB1 and sarcopenia: To understand PGC1α4 expression levels and its cellular distribution in muscle under aging‐associated sarcopenia, we investigated GAS muscle from young or aged mice and found significantly decreased PGC1α4 mRNA and protein levels in aged mice (Figure 1e and Figure S1A), accompanied with reduced levels of phosphorylated cAMP responsive element binding protein (CREB), a master transcriptional regulator for skeletal muscle hypertrophy (Figure 1f).