The process of transferring reducing equivalents from the cytosol into the mitochondria; NADH is used to synthesise glycerol 3-phosphate in the cytosol; this compound is then transported into the mitochondria where it is converted to dihydroxyacetone phosphate (DHAP) using FAD; DHAP then returns to the cytosol to complete the cycle. (Gene Ontology, GO_0006127)
