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.