There is an unlimited number of ways to organize a circuit workout. The above workout is organized with upper body, lower body and cardiovascular exercises. By simply doing the above upper body and lower body exercises in such a way, you will be able to rest your upper body muscles while you workout your lower body muscles, but you will never rest your heart. This is how you make the circuit workout challenging to your cardiovascular system as well as your major muscle groups. Studies have shown that mixing a resistance training regimen with a cardiovascular element will increase your metabolism, therefore burning fat and building muscle. The result is a decrease in body fat percentage.