• Intestinal microbial fermentation produces short-chain fatty acids (SCFAs), signalling to skeletal muscle. • In this study we found that 8h exposure to ≥0.5 mM of the SCFA mixture increased PGC1α and Tfam gene expression compared to 10 mM acetate, but only the SCFA mixture's impact persisted at 24h. In contrast, acetate at ≥5 mM and 10 mM of the SCFA mixture increased PPARα gene expression at 8h. • MyH7 gene expression increased at 24h in response to ≥0.5 mM of the SCFA mixture and to ≥5 mM acetate. • Acetate increased immunofluorescence signal of MyHC I at 48h, while 10 mM of the SCFA mixture increased MyHC I at 72 and decreased MyHC II immunofluorescence signal at 48h and 72h. • SCFAs, particularly in combination, show promise in promoting oxidative phenotype in muscle fibre, providing insights for enhancing muscle health in clinical conditions and among endurance athletes.

GraphPad Prism Project, 10