How to Optimize The Phosphagen (ATP-CP) Energy System?
Reading time: 5 min

How to Optimize The Phosphagen (ATP-CP) Energy System?

Reading time: 5 min
Learn more about the fastest energy system in your body.
How to Optimize The Phosphagen (ATP-CP) Energy System?

The body mainly relies on three different energy systems to sustain physical activity and all other processes in the body.

The three energy systems are:

  • The Phosphagen (ATP-CP) Energy System
  • The Glycolytic Energy System
  • The Oxidative Energy System

In this blog, we'll discuss the fastest of the three energy systems — the phosphagen (ATP-CP) energy system.

What is the Phosphagen (ATP-CP) Energy System?

The phosphagen energy system, also called ATP-CP (or sometimes ATP-PCr) energy system, is the fastest and the least complex energy system in the body. It also produces the least amount of energy.

The phosphagen energy system produces energy with a single chemical reaction that transforms one ADP molecule into one ATP molecule (adenosine triphosphate).

This chemical process is triggered by the enzyme creatine kinase and requires creatine phosphate (CP) aka phosphocreatine (PCr) as the high-energy molecule needed to create ATP.

At the end of this process, the body is left with more ADP, an inorganic phosphate (Pi), and energy. This will increase the levels of creatine kinase which wants to produce more ATP, but it can only do so as long as creatine is available.

The phosphagen system uses creatine phosphate to produce energy.

The Phosphagen System Simplified

The chapter above might have been a little complex and reminded you of nightmare days of high school chemistry.

Let's simplify it.

Your body always stores some energy ready to be used (all energy systems do this in various methods).

Some of this energy is stored as ATP in the muscles (there is more ATP in fast-twitch muscles than slow-twitch muscles). Unfortunately, the amount of ATP in the muscles is very low and is consumed within seconds.

To compensate, the body also stores some creatine phosphate (in higher amounts than ATP), which it uses to produce more ATP. This is the ATP-CP system, which can fuel your extreme-intensity exercise for about 5 to 10 seconds before running out of creatine phosphate to produce more ATP.

The phosphagen energy system works in sprintsThe phosphagen system can fuel you for about 5 to 10 seconds.

The Role of Creatine in the Phosphagen System 

Creatine phosphate is created through the process of phosphorylation that involves an inorganic phosphate and creatine. In simple terms, creatine is the molecule that drives this energy system.

If creatine is available, the body will be able to replenish some of its creatine phosphate stores within 1 to 2 minutes. Unfortunately, with each cycle, creatine levels will decrease, ultimately resulting in fatigue.

Nevertheless, this energy system allows athletes to perform intervals of extreme intensity, as long as they take enough time to recover between each expenditure of the ATP stored in the muscles.

As a side note, while the ATP-CP energy system is anaerobic (meaning it doesn't require oxygen), the phosphorylation of creatine does require oxygen. For this reason, some studies suggest that the aerobic capacity increases the efficiency of this system.

Now, as you may have guessed, the number of intervals you can do depends largely on the amount of creatine available to you.

Creatine is stored in the body, primarily in the muscles — about 60% as phosphocreatine and the other 40% as unphosphorylated creatine. The amount depends on your weight and diet, but a man of 70 kg will store about 120 grams. Furthermore, the liver, pancreas, and kidneys produce about 1 gram of creatine per day.

How do you get more creatine?

To increase creatine levels in your body, you need to consume creatine-rich foods, such as red meat, fish, and some dairy products.

Or, you may choose to use dietary supplements — once you understand this system, it becomes clear why creatine supplements are so popular among weight lifters and many other athletes.

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The Phosphagen System in Practice

As the fastest energy system in the body, the phosphagen energy system fuels short bursts (5 to 10 seconds) of high to extreme intensity exercise.

This may include:

  • Full body movements
  • Throwing, kicking, punching 
  • Sprints
  • Weightlifting

To understand how this system really works, think about lifting a heavy weight or making a full body movement and compare this to other types of exercise, such as walking or jogging.

You may be able to walk or run for hours (depending on your cardio levels), but as soon as you make a full body movement or lift a heavy weight, you feel all your energy has drained. This is because this type of movement uses a different energy system.

However trained and efficient your other energy systems may be, you now need to rest for some minutes before you can try to repeat the same type of exercise.

That's the phosphagen system in practice.

Extreme-intensity exercise, such as sprints and lifting weights, relies on the phosphagen (ATP-CP) energy system.

How to Improve the Phosphagen Energy System?

Now that you understand how and when this system works, you probably wonder — how do I improve it?

Since the phosphagen energy system depends on creatine, consuming sufficient quantities of creatine is the first thing to do.

The other important aspect of this system is oxygen availability. While the system itself is anaerobic, the recycling of creatine into creatine phosphate requires oxygen, so improving your aerobic fitness might also help — this also points out another important aspect to understand, which is that all the three energy systems are codependent.

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Finally, you should perform the right type of exercise.

You may want to find a training guru to provide you with detailed guidelines on how to improve the phosphagen system — and that might not be a bad idea — but sometimes there is no need to reinvent the wheel.

Whatever energy system you want to improve, perform exercises that use that system.

If you want to improve your phosphagen energy system, lift weights, do sprints, do martial arts, or engage in any activity that promotes full body movements. As long as you keep at it, your ability to keep refilling your muscles with ATP will naturally improve.

If you want to improve the phosphagen energy system, consume sufficient quantities of creatine, perform exercises that use this energy system, and try to improve your aerobic fitness.


The phosphagen (ATP-CP) energy system is the fastest energy system in your body that fuels short bursts (5 to 10 seconds) of high to extreme intensity exercise.

This energy system relies on the availability of creatine and your body's ability to recycle creatine into creatine phosphate. 

To improve this system, consume sufficient amounts of creatine — that's where dietary supplements come in really handy — and regularly perform exercise that uses this energy system, such as lifting weights or sprints.