The purpose of circuit training is to keep you moving by only allowing you to take minimal breaks between exercises. If you absolutely must rest, you can take 10 seconds to walk around and then start again. Whatever you do, don't stop moving.
This workout is different from other programs you may have followed. For example, it differs from supersets or compound sets, which target one or two specific muscles and work with the fatigue factor of those particular muscles to increase the intensity of your workout. Circuit training, on the other hand, works because it causes you to keep pushing your body aerobically, while still challenging your strength.
IF you're looking to gain muscle mass, lose fat and get faster, this is the program for you.
First, it allows you to work your aerobic system while simultaneously working on your strength. Since you are constantly progressing through the workout, you will keep your heart rate up, therefore reaping the same benefits as the guy who mindlessly logs all those miles on the treadmill. You, however, will be constantly stimulating your mind, which will help keep boredom at bay.
Second, due to fewer rest periods, you will increase the amount of testosterone you release, which serves to help your muscles grow. While it is true that if you were to perform long aerobic sessions, your testosterone level would drop and you would start to release cortisol (which causes the body to break down muscle tissue), this workout won't take that long to complete. Therefore, you won't reach the time required to start this cortisol-releasing process.
Finally, since you will move through this workout quickly, you won't have to spend long hours in the gym, and you will be able to spend your time doing the things that you never seemed to have time for when you were making the gym your second home.
This is not the only step you need to be gain muscle and lose fat, marry this with our nutrition advice to get a full workout experience.