Energy Systems

Includes the ATP/PC system, the lactic acid system and the aerobic system.

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The ATP/PC System

The ATP/PC system provides energy via coupled reactions, to resynthesis ADP back into ATP. When ATP levels fall and ADP levels increase this stimulates the release of the enzyme creatine kinase, which breaks down the PC bond releasing energy . This energy is not used in muscular work but is coupled to the resynthesis of ADP back into ATP.

The ATP/PC system works anaerobically and takes place in the sarcoplasm of muscle cells. With only one PC resynthesising only one ATP it can only supply energy to resynthesis for 3-10 seconds during an all out maximal sprint.

Training which overloads the ATP/PC system increases the body's muscle stores of ATP and PC. This delays the threshold between the ATP/PC and the lactic acid system and thus increases the potential duration of high intensity exercise for up to 1-2 seconds.

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Advantages and Disadvantages of the ATP/PC System


  • PC stored in muscle cell as readily available energy source.
  • Simple/small compound so very quick reaction/resynthesis of ATP 
  • Does not require oxygen
  • Automatically stimulated by a decrease in ATP and increase in ADP
  • Provides energy for explosive high-intensity exercise/movements
  • No fatiguing by-product 
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