Atp/pc system- ATP is hydrolysed into ADP + Pi, the free phosphate is used in exercises of 2-10s such as a powerlift.Anaerobic energy system- Glucose is the fuel for energy of glycolysis- used in exercises of 10s-3mins such as 400m Aerobic energy system- glycolysis +3 stages ( That I would use diagrams to explain)- used in exercises of low intensity and long duration