“Anaerobic” means not requiring oxygen. Anaerobic bacteria do not need oxygen to grow; in fact, oxygen is usually toxic to them. Fungi and yeast are anaerobic organisms. An anaerobic environment lacks oxygen. Anaerobic exercise relies on the metabolism of the sugar glucose to produce energy which uses “anaerobic pathways” which do not require oxygen. Weight lifting which leads to “burn” is an anaerobic exercise. Human metabolism is both aerobic and anaerobic.