The anaerobic system consists of several energy systems that generate ATP without the aid of oxygen. The anaerobic system is responsible for generating ATP when the intracellular supply of ATP has been depleted. It will generate ATP until the aerobic system is activated and able to meet energy demands. The anaerobic systems can generate ATP at a higher rate than the aerobic system and start up more quickly. The greatest disadvantage of the anaerobic systems is that they are quickly exhausted. In addition, when exercise intensity is too high for the aerobic system to generate ATP quickly enough, the muscles are inhibited by acidosis because H+ ions are released faster than the aerobic system can use them in the oxidative fosforylation.

There are 2 anaerobic systems that generate ATP, the ATP-PCr system in which phosphocreatine also known as creatine phosphate helps in resynthesizing ATP and the anaerobic glycolysis. Phosphocreatine is able to resynthesize ATP by donating its phosphate molecule to an ADP molecule with the aid of the enzyme Creatine kinase and regenerating ATP.

The anaerobic glyolysis breaks down glucose or glycogen to convert ADP through a series of reactions back to ATP. The anaerobic glycolysis also needs an ‘investment’ of ATP for some of these reactions to complete the cycle. The products at the end of the cycle such as pyruvic acid and lactic acid can be of further use in the aerobic system where they are broken down further to generate more ATP.

References:
-Baechle, T.R., Earle, W.R. (2008). Bioenergetics of Exercise and Training. Essentials of Strength Training and Conditioning. Third Edition. USA. Human Kinetics.