Mitochondrial lactate dehydrogenase (mLDH) and monocarboxylate transporter MCT1 are detectable in human skeletal muscle mitochondria, but their detection is contingent on isolation techniques, and contamination by cytosolic components is a persistent methodological issue.

Lactate enters muscle mitochondria through a transporter on the outer membrane, where it is converted to pyruvate by an enzyme attached to the inner membrane. This conversion uses energy from the electron transport chain to proceed, and the resulting pyruvate moves into the mitochondria's inner compartment to fuel energy production. The same transporter also moves pyruvate inward. Contamination from the cell's fluid can falsely appear as if these components are inside mitochondria when they are actually from outside.