During exercise, we use a combination of aerobic glycolysis and aerobic lipolysis sources.
•At a high intensity the main source of energy is carbohydrate and at a low intensity fat is the predominate source.
•As there is a limit to the amount of carbohydrate that can be stored in the muscles, high intensity work can only be sustained for short periods.
•We have large stores of fat so low intensity work can be maintained for long periods.
Oxygen energy system