The aerobic energy system is your diesel-powered semi-trailer. It takes a while to warm up, but once it is going, it goes the distance producing plenty of ATP with great efficiency.

This energy system uses fats, carbs, and protein to produce plenty of ATP, but produces them at a slower rate compared to the two anaerobic systems. This system produces water and carbon dioxide as a waste product, which are easily removed through the cardio-vascular system. Fatigue occurs as cabs run low and the muscle relies more on fats for ATP production. This requires more oxygen per ATP and so requires an increase in systems needed to deliver more oxygen to the muscle. This is often termed “hitting the wall” and requires the body to make adjustments in the cardio-vascular system and a short-term reliance on anaerobic systems.

The aerobic system predominates in most sports, but especially in endurance events, such as marathon running. The world record for marathon (40Km) is currently 2:02:57. At just over 2 hrs this event relies heavily on the aerobic system utilising the other systems only when a sprint is needed, often to the finish. This event would deplete glycogen stores and rely on fat for ATP production about half way through. This event requires consistent ATP production and demands the delivery of plenty of O2 in order to complete it.