The two main types of anaerobic respiration are alcoholic fermentation and lactic acid fermentation. These methods of respiration occur when the amount of oxygen available is too low to support aerobic respiration.
Alcoholic fermentation converts glucose into ethanol. In alcoholic fermentation, glucose is broken down by glycolysis, and two ATP molecules are released in the process. The pyruvic acid molecules produced during glycolysis break down into ethanol and carbon dioxide. In animals, the process of lactic acid fermentation, similarly, occurs after the glycolysis process. Pyruvic acid is changed into lactic acid, and muscle tissue is broken down by lactic acid. Lactic acid fermentation is the reason that muscles burn during an intense or long workout. Lactic acid breakdown of muscles results in muscle tissue rebuilding itself to become stronger.