Anaerobic Biochemistry

Anaerobics are activities that are carried out 'without oxygen'. This terminology refers to the molecular level of respiration, not the respiration of the organism as a whole (i.e., breathing). During anaerobic exercise, the muscles being exercised have insufficient oxygen to meet the demands of the activity, and thus must also use alternate, non-oxygen-dependent processes to produce energy. The muscle does still receive oxygen during anaerobic exercise; the average drop in blood oxygen content throughout the body is likely minimal.

Anaerobic exercise begins with muscles utilizing stored creatine phosphate to generate the ATP that produces muscle contraction. After several seconds, further ATP energy is made available to muscles by metabolizing muscle glycogen into pyruvate through glycolysis, as it normally does through the aerobic cycle. What differs is that pyruvate, rather than be broken down through the slower but more energy efficient aerobic process, is fermented to lactic acid.
Muscle glycogen is restored from blood sugar, which is either released from the liver, from digested carbohydrates, or amino acids which have been turned into glucose.