What is ATP?

"What is ATP?" is an important question in sports training because all energy production is powered by this compound. The training programs you design for your athletes will target their ability to produce energy for power and/or endurance.

ATP is often referred to as the energy currency of life. The body’s cells use a special form of energy called adenosine triphosphate (ATP) to power almost all their activities, such as muscle contraction, protein construction, transportation of substrates, communication with other cells, activating heat control mechanisms, and dismantling damaged and unused structures.

Every cell has a small store of highly charged ATP located in the cytoplasm. ATP is made up of adenosine and three inorganic phosphate (Pi) groups bonded together in sequence. Each of the phosphate bonds stores the energy the cell can use. The bond between the second and third phosphate groups contains the most accessible energy.

When an enzyme breaks off the third phosphate group from the second phosphate group the energy is released so the cell can use it. When this happens the ATP becomes an energy deficient adenosine diphosphate (ADP). That is, there are only two phosphate groups bonded in sequence rather than three.

In order to reattached the third phosphate group back onto the second phosphate group (in the process converting the energy deficient ADP back into high energy ATP) a fuel source containing energy is needed. This fuel source comes from the food we eat.

The sun is the original source of the fuel the body uses to convert energy deficient ADP back into high energy ATP. Plants convert sun energy into carbohydrates, fats and protein. Humans eat the plants and they also eat other animals that also eat the plants.

The digestive system breaks the ingested food down into tiny units called amino acids (proteins), glucose (carbohydrates) and fatty acids (fats). These tiny units are absorbed into the bloodstream and transported into the cells. The cell can use the tiny units as fuel to convert ADP into ATP and for building and strengthening all its structures. Without the ability to remake ATP the cell would run out of its ATP supply after a couple of seconds.

The mechanisms responsible for reconnecting the phosphate group onto the energy depleted ADP to reform the charged ATP are referred to as the body’s energy systems or energy pathways. One ATP production mechanism (consisting of two different strategies) can remake ATP without using oxygen and is therefore called the anaerobic energy system.

The other ATP production mechanism needs oxygen and for this reason is called the aerobic energy system. As soon as the phosphate group is broken off from an ATP to release the energy these two broad mechanisms kick into action to reconnect the third phosphate group back onto the energy depleted ADP to remake the high energy ATP. The cell protects its ATP store and will not let it drop below 60%. Recharging ADP back into ATP is an ongoing process.

The information and illustrations about "What is ATP?" are courtesy of Dr. Christine Brooks. For more about training your athletes' energy systems for peak performance, see Training High Performance Athletes.

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