© by David~O

The ATP-CP system consists of two energy storage reservoirs:

  1. ATP (adenosine triphosphate)
  2. Creatine Phosphate (CP)


The primary energy reservoir is ATP. ATP storage capacity in the body is 80g-100g and provides energy for maximal output for 1-3 seconds, depending on exercise intensity and the individual’s body size (bigger people store more energy and can produce more force; mass moves mass principle). The body doesn’t like to keep a lot of ATP stored because it’s such a heavy molecule. Instead, the body prefers to have a small amount of ATP stored, use it, and reformulate it, use it, and reformulate it, so there is a constant cycle of keeping just enough ATP in the system. Otherwise if one had to store enough ATP to last for an entire day, body weight would increase dramatically. It takes about 90 seconds to replenish ATP.

Creatine Phosphate

The secondary energy reservoir is creatine phosphate. The body stores 320g-600g of creatine phosphate and provides energy for maximal output for up to 10 seconds, depending on exercise intensity and the individual’s CP stores. The recycling of ATP with the help of creatine phosphate is the simplest and hence quickest way since it only requires one enzyme, creatine kinase, to facilitate the reaction. Basically, creatine phosphate is hydrolyzed (H2O) with the help of the enzyme creatine kinase and thereby provides the energy to form ADP and inorganic phosphate. In other words, the energy derived from the breakdown of creatine and the phosphate molecule will drive the inorganic phosphate into the sarcoplasmic solution, where it attaches to ADP with the help of the enzyme ATP synthase, thereby forming ATP. So, the exergonic reaction, hydrolysis of creatine phosphate, provides the energy so that the endergonic reaction, the synthesis of ATP, can occur and the enzyme ATP synthase facilitates that ATP formation process. Now, once energy is required to perform work, ATP will be broken down via hydrolysis (H2O) with the help of the enzyme ATPase, and ADP remains left over in the sarcoplasm and the rephosphorylation process (breaking down creatine phosphate) repeats itself.

ATP Production Cycle via Creatine Phosphate

CP + H2O —- creatine kinase—> ADP + inorganic phosphate ——ATP synthase—-> ATP + H2O —-ATPase—-> ADP + energy

  1. Hydrolysis of CP via creatine kinase, which provides a phosphate molecule
  2. Condensation of ADP & phosphate; ADP picks up the phosphate molecule and synthesizes ATP via ATP synthase
  3. Hydrolysis of ATP occurs to release energy for muscle contraction
  4. ADP is left over and needs another phosphate molecule to reform ATP


Creatine phosphate reproduction, called rephosphorylation, requires ATP and only occurs during recovery. Even though ATP replenishment only takes 90 seconds, CP takes 2-5 minutes to replenish because one has 4-6 times the amount of creatine phosphate (CP) stored than ATP. Because creatine phosphate is used to form ATP, it is helpful to take large amounts of creatine supplements to increase creatine phosphate stores, thereby improving short-term high-intensity exercises. The ATP-CP system provides energy for muscular contraction at the beginning of exercise & for short-term high-intensity bouts up to 15 seconds.


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