How does fermentation allow glycolysis to continue?

Fermentation allows glycolysis to continue by regenerating NAD+ from NADH. Since glycolysis requires NAD+ to function and produces NADH, the lack of oxygen (which would typically enable NADH to be oxidized in the electron transport chain) limits NAD+ availability. Fermentation pathways, such as lactic acid fermentation or alcoholic fermentation, recycle NAD+ from NADH, allowing glycolysis to continue.