Energy metabolism in the skeletal muscle. Glycolysis represents an oxygen-independent source of ATP and pyruvate. Pyruvate is reduced in the cytosol to form lactate or oxidised in the mitochondrial matrix to form acetyl CoA, which feeds into the TCA cycle. β-oxidation of fatty acids and the TCA cycle produce reduced intermediates, NADH and FADH2, which are oxidised by complexes of the electron transport chain. Electrons are transferred to the final oxygen acceptor, O2, and the free energy from this process is used to pump H+ ions into the intermembrane space. The resulting electrochemical gradient is the driving force for the oxidative phosphorylation of ADP. ETF electron-transferring flavoprotein, I-IV complexes of the electron transport chain, F
subunits of the ATP synthase, NADH β-nicotinamide adenine dinucleotide reduced, NAD β-nicotinamide adenine dinucleotide, C
acetyl CoA with carbon chain length n, FFA free fatty acids. Figure adapted from .