Source of Fuel – The alactacid energy system or ATP/PC (Adenosine Tri-Phosphate/Phospho-Creatine) energy system uses the ATP that is immediately available within the muscle cell (myocyte). As the ATP id broken down into ADP and P, the ADP reacts with the PC (without the presence of oxygen) in the myocyte to produce another ATP and C (1 ATP per PC).
Efficiency of ATP Production – The alactacid energy system (ATP/PC) has a very fast rate of ATP production, but has a very limited store of fuel. The PC runs out quickly resulting in this system no longer being available until it has begun to recover.
Duration that the system can operate – The alactacid energy system (ATP/PC) does not last very long due to the limited fuel source and fast ATP production. The alactacid system will deplete its fuel in 8 seconds when used at maximal intensity, but can take as long as 12 seconds if used at a lower intensity.
Cause of fatigue – Fatigue in the alactacid energy system (ATP/PC) is caused by the depletion of fuel. Once the immediate stores of ATP and PC run out the system needs to recover before it can be used again.
By-products of energy production – The alactacid energy system (ATP/PC) has no by-products other than heat, which is a by-product of every energy system.
Process and rate of recovery – The alactacid energy system (ATP/PC) recovers as the creatine in the cell connects to the free phosphates again, storing them as PC to be used when they are needed again. This process takes up to 2 minutes for complete recovery, but can be half restored at around the 30 second mark.
Examples – Due to the speed of ATP production and the short duration of the fuel source the alactacid energy system (ATP/PC) is the dominant system in activities such as a 100m sprint, discus, javelin, high jump and other sports of very short duration. However the alactacid energy system (ATP/PC) is also used to provide brief periods of high intensity within many other sports. Examples include kicking a ball during soccer or rugby league, or a short sprint where maximal effort is needed, but lasts only 5-10 seconds.