The three energy systems do not work in isolation but in fact work together to produce energy for the body. At any given time throughout the activity there is at least more than one energy system contributing to ATP production. The percentage amount of energy that a system produces will determine if it is predominant energy system being used. By saying that an energy system is predominant at a given moment in an activity you are saying that a particular energy system is supplying the majority of energy demands.

(Image from jacaranda textbook, Live it Up 2 PE)

The graph above shows the relative energy contribution of the three energy systems during maximal activity. At the start of an activity ATP stores within the muscle will be used until depleted. the ATP-CP energy system will then begin and will contribute the majority of energy as it can produce energy at a very fast rate. However creatine phosphate stores(CP) are limited within the body and these will quickly run out (around 10 seconds)resulting in the steep reduction in contribution by the ATP-CP energy system.

The anaerobic glycolysis system will soon become dominant after the ATP-CP energy system as it does not require oxygen so it becomes the dominant energy system when CP stores are low and when the acute responses needed to get the oxygen in for the aerobic energy system have not quite come into effect to efficiently provide the needed oxygen.The anaerobic energy system typically comes into effect at around 8 seconds and will remain dominant until around 75 seconds of an activity.

The aerobic energy system will become dominant after about 75 seconds and will remain dominant throughout an activity. If intensity is increased throughout an activity the aerobic system will remain dominant but there will be increased energy contribution from the two anaerobic pathways.

## An energy system interplay example

For example a question in the exam may ask you to describe the energy system interplay involved within a 15 minute quarter of netball.

For these types of questions it helps to begin with a general sentence such as ‘throughout the activity more than one energy system will be contributing to energy production throughout the activity.’ It is important in your answer that you make reference to both the intensity of the action being performed and the duration as both of these factors will influence which energy system would be used for those types of movements. Make sure that your answer is specific to the given scenario in this case it is netball but it may be volleyball, surfing or bike riding and you should try to have a general knowledge of the different kinds of activities used in those sports.