Human body has three different energy systems, which are:

• Anaerobic Alactic
• Anaerobic Lactic
• Aerobic

Every process in our body needs energy, ATP (Adenosine Tri Phosphate). The quantity of ATP in each muscle is sufficient for a 2-3 seconds activity. Our body also keeps CP (Creatine Phosphate, you might heard of the Creatine supplement), which is used to regenerate ATP. CP has enough energy for 4-5 seconds. Therefore, ATP + CP altogether has enough energy for about 8 seconds. ATP + CP together called Anaerobic Alactic Energy System. By its name we can understand that this process doesn’t require oxygen (anaerobic) and produces no lactic acid (alactic). This is main source of energy for activities involving bursts of high-speed or high-resistance movements lasting up to 10 seconds.

The next energy system is Anaerobic Lactic. It also doesn’t require oxygen, but produces lactic acid. Anaerobic lactic uses muscle carbohydrate (glycogen stored in the muscle) and it is chief source of energy for activities lasting between 10 seconds and 2 minutes (peak output for this system occurs in all-out efforts of about 30 seconds).

Last energy system is Aerobic (aerobic literally means "with oxygen"). In opposite to the previous two energy systems it requires oxygen (produces no lactic acid). It is the main source of energy for activity lasting more than 2 minutes for prolonged continuous or prolonged intermittent effort. Uses carbohydrates and fats for fuel, and the blood bring this fuel to the muscles from outside the muscles.

An image demostrating the afore mentioned: