The body produces energy in the muscle cells though a process called unbonding and bonding. When we engage in muscular activity, the most immediately usable chemical is adenosine triphosphate (ATP). In part, the foods you eat are converted to ATP, which is then stored in most body cells.

ATP is a chemical substance that consists of one molecule of adenosine connected to three phosphate molecules by high energy bonds. Whenever you want to contract a muscle, your body sends a signal to your cells indicating that energy is needed. When the cells receive this signal, they break down molecules of ATP to create energy.

When this process occurs within an ATP molecule, the high-energy bond between the adenosine molecule and one phosphate molecule is broken, and energy is released. The energy produced by this chemical “unbonding” assists with a variety of processes in the body, including muscle contractions.

Where does the body get ATP? The answer is the three energy systems discussed energy production I. The three energy systems through which the body can get and use ATP are the start-up, the three minute power system, and the endurance system. The body will use these systems depending on the intensity and duration of the activity you’re doing. Generally, the body will proceed from one system to the next in sequence, with a small amount of overlap.

Energy System I: The start up system aka ATP-PC system or anaerobic phosphagen system.

The startup system breaks down the stored ATP for immediate, short-term use in the muscles. The term anaerobic means “without oxygen” This ATP is used up after about 10 seconds of intense exertion. The body then creates or manufactures more ATP by breaking down another chemical called phosphocreatine, or PC. PC can be obtained from the foods you eat just like ATP. PC is stored in cells throughout the body.

The body stores only small amounts of ATP and PC in the cells at one time. Therefore, the amount of potential energy from this source is limited and can be used only for activities that require short, intense bursts of muscle strength, such as judo throws, weight lifting or start of race. Thus, the start up system can supply energy only for a short time. After that system runs out of energy, the body must find another way to get the energy it needs.

Energy System 2: The three minute power system a.k.a anaerobic glycolysis

Exhaustion of the energy system I lead into energy system II. The body switches over to the three minute power system. The term glycolysis means “the breakdown of glycogen (stored carbohydrate) or glucose (blood sugar)”. In the three minute energy system, the body manufactures ATP by breaking down glycogen or glucose. ATP is then broken down partially to provide energy.

In anaerobic glycolysis, the body only partially breaks down the glucose to create energy, leaving behind a by product call lactic acid. As the breakdown of glucose continues, lactic acid begins to accumulate around the muscle tissue. After about 3 minutes of activity, the accumulation of lactic acid around the muscle tissues creates sensations of discomfort and muscle fatigue and also prevents from reforming ATP. It is jogging when you are out of shape you quickly begin to feel a cramping and muscle discomfort which causes you to stop. The problem as well may be that lactic acid may mislead you in thinking that you have reached your limits. As you become more conditioned these sensations take a longer time to occur, you may feel a twinge of fatigue as lactic acid builds up.

Anaerobic glycolysis can only provide intense energy for brief periods of time. Ju-jitsu, Kata, gymnastics are few examples of activities that rely heavily on anaerobic glycolysis of energy. As you continue training, your body will call on its next energy system, the endurance system, to provide more energy.

Energy System 3:The Endurance System aka the aerobic system or metabolism