The reserves of this compound in the muscle can only provide energy for five to eight seconds. The benefit of the process is to allow the muscles to react instantly. This avoids waiting for the cardiovascular system to provide the extra oxygen that the aerobic pathway needs to work. Like ATP, creatine phosphate must be rebuilt when depleted. Rebuilding creatine phosphate uses some of the energy liberated from ATP and the aerobic pathway.
Anaerobic glycolysis is the second process that supplies energy to the muscle fiber without oxygen.
Gycolysis is the breakdown of sugar. Anaerobic glycolysis is an intermediary energy source used after the creatine phosphate is depleted but before the aerobic pathway starts. Enzymes transform glucose into pyruvic acid and make ATP in the process. If the muscle fiber has enough oxygen, the pyruvic acid enters the mitochondria for further energy use. But if the muscle fiber lacks sufficient oxygen, the pyruvic acid cannot enter the mitochondria and changes into lactic acid .