What is the definition of the alactic energy system?

Answer 1

There are four major energy systems for the human body. One is aerobic -- it needs oxygen to function. The other three are anaerobic -- they can function when the body is in oxygen debt (it doesn't have enough oxygen to supply all needed energy through the aerobic system). One of those anaerobic systems simply uses the available "fuel" (ATP) and is only good for a few seconds. The other two of those three anaerobic systems can resynthesize ATP. Of those two, one produces lactic acid as a byproduct. The other one doesn't, so it is "alactic."

The fuel is created by releasing the 3rd hydrogen molecule (ATP is made of one adenosine and three phosphate molecules). ADP is the result where there are only two hydrogen molecules remaining. PC replaces this lost molecule, hence the given alternative name ATP/PC system. ATP or adensoine triphosphate is a high energy molecule.