The intensity of the play dictates the predominant energy system supplying ATP. An example of this is when the player carries the ball into contact and works at a high intensity, the ATP-PC system is the predominant energy system. As exercise intensity increases then so does heart rate and lactic acid.
This is referred to as DOMS, Delayed Onset Muscle Sorenes. The exact mechanism is not understood, but DOMS appears to occur due to connective tissue microtrauma.
