series of reactions strips its highest-energy electrons and uses them to form a small “carrier molecule” known as an NADH. If glucose is like a shipping container, then NADHs are like delivery trucks. The process of loading the electrons into the trucks is called glycolysis. It’s ancient; in fact, it’s how yeast cells harvest energy. When glycolysis occurs in the absence of oxygen, it is known as fermentation. If your muscles are pushed to their limit and there’s not enough oxygen in your bloodstream, your cells ferment glucose as a stopgap measure for energy production.
