Muscular contractions require energy from our bodies, this energy is in the form of a molecule called ATP. However the body has three generation systems which it uses to create ATP. In aerobic states, when oxygen is plentiful in the body, the three generation systems (Glycolysis, Krebs Cycle, and the Electron Transport Chain are able to operate. The difference between aerobic and anaerobic. Once your ATP demand exceeds the ability of the body to deliver oxygen to run these processes, you enter an anaerobic state, in which only Glycolysis can continue to operate. Once byproducts build up, lactic acid forces this anaerobic activity to a stop. Anaerobic means, without oxygen.

Is the electron transport chain aerobic or anaerobic? It is aerobic
is the krebs cycle aerobic or anaerobic? It is aerobic
is glycolysis aerobic or anaerobic? It can be both