Adenosine triphosphate, commonly known as ATP, is one of the major energy sources for every cell in the body. A cycle of energy production occurs in each cell mitochrondria, the energy producing factories in cells. Fat cells and muscle cells contain many mitochondria. Fat cells store a lot of energy, and muscle cells often need a lot of energy on short notice. All cells need a constant supply of energy to maintain functions and for repair and replenishment. This is gained from foods eaten.
Respiration is another important component of energy production through ATP, which is why aerobic exercise can provide sustainable energy. It increases the body's ability to make ATP quickly as a source of energy.
When considering how ATP is used, understanding the cycle of ATP and oxygen exchange is an important element for a maintaining a healthy body and consistent reserves of energy.
ATP – Potential Energy
ATP is made of adenosine and three phosphate bonds. The phosphate bonds are high energy, meaning that when they are broken, a large amount of energy is released for use by the body. Having a ready supply of ATP means there is energy available that can be harnessed when needed, much like having a surplus of money in the bank. The reserve awaits a need. Going on a hike up a steep mountain trail, for example, is a lot more easily accomplished with a healthy supply of ATP than without.
How ATP is used by the body is largely due to high energy bonds, which can be broken by ATPase, an enzyme specifically present to break the third phosphate bond. Breaking this bond releases a large amount of energy, and ADP, or adenosine diphosphate, remains. ADP can be converted back to ATP by bonding to another phosphate group. This can occur by eating foods which, when broken down, release phosphate. The phosphate from foods then bonds with ADP, making ATP once again.
A small amount of ATP exists in muscle cells and provides energy for several muscle contractions. The cycle of ATP to ADP and back to ATP provides a continual supply of energy. This occurs in the presence of oxygen and food which provide the elements needed for continual chemical reactions. Under anaerobic conditions, oxygen will be used rapidly, and the body will begin drawing from anaerobic sources. This is short-lived, since the cycle of ATP-ADP requires oxygen and phosphate.
After hard exercise, such as weight lifting or bike racing, food is required, since the energy stores will be used up. Gasping of breath or rapid breathing is often experienced as a way to replenish the oxygen levels in the body.