What is ATP?
What is ATP is a question that I get asked a lot. Most athletic have an understanding of what ATP is and that it provides the energy they need to perform. In my article Food: Nutrition Absorption and Delivery I discussed that after we eat a meal, the nutrients are digested, absorbed and screened by the liver and then sent into the bloodstream of the body to reach target cells. Once the nutrients reach their target cells a number of things can happen such as: 1) they are oxidized for energy production, 2) they are transformed and incorporated into the various components of the body, 3) they are stored for future energy needs, and 4) they are eliminated from the body. To answer what is ATP is to focus on nutrients being oxidized for energy.
The Laws of Thermodynamics and ATP
Before answering “what is ATP” let’s first take a high-level overview of the laws of thermodynamics. When we are talking about energy production in the human body we are really not talking about producing energy. The laws of thermodynamics state that energy is never created and energy is never destroyed, but rather that energy is transferred between to entities. This energy transfer usually results in one entity losing energy while the other absorbs that energy. Therefore, the net energy between that two entities is still equal.
Now taking the laws of thermodynamics and applying them to our body is no different. We gain the energy we need to live by the food stuff that we eat. The energy to supply our metabolic function comes from the energy that is stored in the food. Through the digestive process the breaking down the bonds between the carbon and hydrogen molecules creates a burst of energy. This burst of energy is the first step in the production of ATP. This initial energy burst is the energy transfer from the carbohydrates, proteins, and fats into the formation of ATP.
What is ATP and How is it Produced
ATP is Adenosine Triphosphate. ATP is needed for almost every action within our body. ATP is required for muscle contraction, proper functioning of our digestive system, to produce various enzymes, and ATP is even required to create more ATP. Because ATP is needed in such high demand, energy production is focused on the rebuilding of ATP molecules once they are broken down and used for energy. Although our bodies can make more ATP from new nutrients that we eat, ATP can also be created from the stored nutrients in our liver cells (hepatocytes), our muscle cells (myocytes), and in our fat cells (adipocytes).
Interestingly, it is the stored nutrients that supply the major bulk of the energy that we require to produce the ATP to function in our daily lives. However, when it comes to long endurance exercise, our ATP is not created from these stored nutrients. Endurance exercise requires a lot of energy (and ATP) so our muscles must not only tap into the stored nutrients, but also must tap into the recently absorbed nutrients to be able to sustain a long duration of exercise.
If we are not participating in a long endurance type event, then most of the energy to create ATP that our body will require come from stored nutrients. This is even true for moderate exercise bouts. The two most important of these stored nutrients are trigylcerides and glycogen, because they are the first to produce more ATP when the body needs it. Not only do they have to provide the energy for the cells that they are stored in, they must also supply energy to those cells that can’t store their own energy. These include such cells as our red blood cells and cells in the brain. So, when our cells call for the production of more ATP, it is from our stored triglycerides and glycogen.
When we are exercising our bodies require a constant supply of ATP for muscle contraction. Therefore, metabolic pathways, or Energy Transfer Pathways; must exist within our muscle cells with the ability to produce ATP rapidly. There are three methods that our muscles produce ATP: 1) ATP/CP Pathway, 2) Glycolytic Pathway, and/or 3) Oxidative Pathway.
