MYH7 and sarcopenia: Skeletal muscle fiber composition is a critical determinant of muscle quality and metabolic function.41 Accumulating evidence indicates that gut microbiota modulates various skeletal muscle traits, including muscle mass, sarcopenia,42–44 and muscle fatty acid deposition and meat quality in livestock.45,46 In this study, we demonstrate that gut microbes influence skeletal muscle fiber transition by elevating the methyl donor metabolite betaine, enhancing m6A RNA methylation, and specifically upregulating Myh7 expression in a murine model.