A few days ago, I did something called circuit training. Circuit training is a form of mixed exercise that combines cardio and strength training into one. Almost every muscle group in your body comes into play. If you saw the manner in which I was panting; you would not doubt that my heart and lungs were clearly in play. Any good physical instructor will tell you that this is the ideal form of exercise; one in which your muscles, lungs and heart are all activated all at the same time.
The purpose of any exercise is exactly that. To build the capacity of your lungs to take in more oxygen. To build the strength of the muscles of your heart and to develop the power of your different muscle groups. You could perform each of these in isolation. For example, I could repetitively use a brick that weighs say five kilogrammes to perform a bicep curl. The action of lifting the brick will build the muscles in my arms. Performing a single act that exercises a single muscle group is called an isolation exercise. Of course, your arms will get stronger. However, unless you are extremely unfit, it is unlikely to bring into play either your lungs or heart. Also, no other muscle group in your body will develop.
A compound exercise, on the other hand, attempts to bring everything into play. For example, you may do a bench press which works out the muscles in your chest, shoulders and triceps simultaneously. If you mix this up with some form of exercise that also works on your lungs and heart, for example, Tabata, you multiply the benefits.
The outcome is greater fat burning, overall development of your muscle groups and a stronger heart and lungs.
I needed to be lifted off the floor once I finished my circuit training; it was that exhausting. Two hours later, I felt I was invincible. Try me!