ATP: The Body's Energy

When it comes to the exercise world, adenosine triphosphate, or ATP, is cream of the crop for muscular contraction and cell life.  To us trainers, ATP is known as the universal energy donor because it can couple the energy released from the breakdown of foodstuffs into usable energy for cells. (1) As important as ATP is , it is important to note how our bodies produce this molecule.

An ATP molecule.

Muscles already have a storage of this ATP molecule, but exercise demands a very large amount of ATP to provide contractions (look for this blog in the future), but the storage alone cannot meet the demand.  For our bodies to get this ATP we have three metabolic pathways: the combination of ATP and phosphocreatine, or the ATP-PC system, breakdown of glucose or glycogen known as glycolysis and finally oxadative formation. (1) The first two pathways are known as anaerobic, meaning it does not require oxygen and the third is aerobic, meaning it does require oxygen.

Sprinters use the ATP-PC system in their short, but intense journey

Inside our muscles, a small store of phospocreatine (PC) and ATP exist to provide energy for muscle contraction at beginning of exercise and energy for short, high intensity exercises, which usually lasts less than 10 seconds.  Athletes that are sprinters, or power lifters rely on this ATP-PC system to provide their short, intense actions, but someone like a football player making a dash at the goal line, or a baseball player trying to beat the throw to first base also rely heavily on this system. This system does not require oxygen.

Lifting those weights leans heavily on the process of glycolsis.

The second energy system is called glycolysis   Glycolysis involves the breakdown of glucose and glycogen through a very complex series of metabolic actions ending in the formation of ATP. Glycolysis offers sufficient energy for actions lasting from about 10 seconds to about 2 minutes. This is the energy system weight lifters primarily use, since a set of work usually lasts about 30-90 seconds of exertion. This system does not require oxygen.

Swimming and other long duration exercise utilizes the oxidation process.

The final energy system is what we call the aerobic ATP production or oxidative phosphorylation (OP).  Unlike the other two systems, this process requires oxygen, through means of the very complex Krebs cycle then through the electron transport chain. The end result of the ETC is the formation of water and ATP, which is why we breath oxygen.  OP kicks in after about 2 minutes of exercise and is primarily used for continual, low intensity actions such as jogging.  This is the main system we tend to use at rest as well.

In order to win this race, your body would have to use all three phases of the bodies energy system accordingly.

Now, here's the kicker, these energy systems do not function as a single system, they work in conjunction with each other. You see, in order for glycolysis to begin working for the weight lifter, the ATP-PC must activate for the first for seconds, then when the storage is used up, glycolysis is called upon to continue the action.  In order for the OP system to begin working for the jogger, their ATP-PC storage is used up in the first few seconds, then glycolysis takes over for two minutes, then finally aerobic ATP is active to allow for the continual movement. (please note that at 2-3 minutes of exercise a 50/50 split of anaerobic and aerobic occur) Although the systems never truly just stop working you can think of it like this:

ATP-PC (1-5 seconds)>>>>>> Glycolysis (up to 2 minutes)>>>>>>>>OP (used the most after 2 minutes) 

In order to get to the next system you'll go through the previous one first until the energy system for a particular exercise is optimal.  You may primarily use oxygen and the OP system when you go jogging for an hour, but you must use the ATP-CP and glycolysis systems as you begin and continue to jog.  The whole process of combining the three systems is more integrated and complex than an entire website devoted to the subject.

Take a look at how complex glycolysis and Oxidative Phosphorylation truly is to produce the energy we require for exercise. (Photo courtesy of inoxx.net)

As you can see, the body has a very complex and diverse system(s) to provide cells and skeletal muscles energy to allow for the desired exercise or movement we wish to perform.  Our body's method of generating this ATP molecule is a very large process(s), even though I have provided a nutshell version, please do not think this is as simple as it looks.  Through a natural storage, conversion of foodstuffs and our breathing of oxygen, our body finds ways to supply us with the energy needed not only for sport, but for life itself.  The next time you begin a particular exercise, think for a moment what type of energy system you might be using the most and you may then be able to strategize what type of food and training needed to maximize your results.

"No! Try not. Do, or do not. There is no try"- Yoda


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References

1. Powers,S. Howley, E. (2007) Exercise Physiology Theory and Application to Fitness and Performance 6th edition (33-48) NY: McGraw Hill

2. Howley, E. Franks, B. (2007) Fitness Professional's Handbook 5th edition (446-447) NY:  McGraw Hill

*I am not a doctor or a licensed physician.  I am in no way diagnosing anything and recommend that you speak to your physician before making any medical decisions.

*I am not a registered nutritionist or dietitian. The information presented is for education purposes only.