Why can mitochondrial myopathies lead to high levels of lactic acid in muscles?

Mitochondrial myopathies can lead to high levels of lactic acid in muscles because of a fundamental impairment in the mitochondria, the cellular structures responsible for producing energy through oxidative metabolism.1

When mitochondrial defects prevent the efficient oxidation of fuels like glucose and fat, the body must compensate to meet energy demands. To provide the necessary energy, the muscles rely on the nonoxidative breakdown of stored [glycogen]. This process is less efficient and results in the accumulation of lactic acid as a byproduct. Additionally, deficiencies in the proteins that form the electron transport chain can lead to the buildup of unused metabolic intermediates, which may further contribute to the generation of damaging substances, including lactic acid.12