How Does the Phosphocreatine Energy System Power Muscles?

Track sprinter
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Phosphocreatine, also known as creatine phosphate, is an energy source for muscle contraction naturally present in the skeletal muscle tissue of humans and other vertebrates. It enables the expression of explosive power in the muscles, lasting no longer than eight to 12 seconds. It is an organic compound of creatine and phosphoric acid with the molecular formulation of C4H10N3O5P

The Phosphocreatine Energy System

The muscles use the phosphocreatine energy system, also known as the anaerobic alactic system, during the first 10 seconds of sustained muscle contraction. It is anaerobic because it doesn't require oxygen to function and alactic because it doesn't produce lactic acid.

The energy system that powers muscle contraction uses adenosine triphosphate (ATP). ATP is produced from glucose through the glycolytic pathway. But little ATP is stored in the muscle and the body uses it up in the first few seconds of muscle contraction. It needs to be replenished using phosphocreatine to convert adenosine diphosphate (ADP) into ATP in the mitochondria of cells in the muscle tissue.

To make ATP, phosphocreatine transfers a phosphate molecule to ADP. The newly-formed ATP is now available to be used for muscle contraction. The leftover portion of phosphocreatine is creatine, which is processed by the liver into creatinine and eliminated through the kidneys and urine. The body doesn't recycle this creatine into phosphocreatine.

The Phosphocreatine Cycle

Muscle fatigue is noticeable by the end of the phosphocreatine cycle. After 10 seconds of muscle contraction, the muscles are able to use anaerobic glycolysis and aerobic glycolysis pathways to provide energy. Phosphocreatine is regenerated by the liver, pancreas, and kidneys.

Fast-twitch skeletal muscles store more phosphocreatine to have available for short periods of intense muscle contraction. The slow-twitch skeletal muscles and heart store less. By middle age, people have lower phosphocreatine stores in their muscles.

How Athletes' Bodies Use Creatine

For sports and exercises that require explosive muscle contraction, there is a lot of interest in maximizing phosphocreatine in the muscles to boost performance. If you have more phosphocreatine in a muscle, you are able to endure a longer period of intense muscle contraction before the muscle is fatigued and loses power. Weight lifting, sprinting, basketball, football, ice hockey, cycling, tennis and field sports could benefit from a longer phosphocreatine phase. Track sprinters over 100 meters use predominantly the phosphocreatine/ATP system of energy production.

Creatine Supplementation to Boost Phosphocreatine

Dietary creatine supplementation can increase the total creatine concentration in the muscles. Naturally-occurring creatine in red meat is one source, although it isn't concentrated enough to boost phosphocreatine levels in the muscles above normal.

To elevate phosphocreatine levels, supplementation with creatine is used. Other nutrients can boost uptake of creatine by the muscles, especially carbohydrates such as glucose and simple sugars. For this reason, low carb diets may not be the best choice for athletes who want to maximize their explosive muscle power. Vigorous exercise also increases muscle uptake of dietary creatine.

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Article Sources
  • Creatine. MedlinePlus. U.S. National Library of Medicine.