Let's look at the squat. It is a compound exercise. It works the quadriceps, hamstrings, gluteus, lower back, abdominals, hips, and abductors. Squats allow for heavy weights to be lifted. This makes the squat an incredibly effective muscle building exercise. Compared to an isolation exercise such as the leg extension, which only focuses on the quadriceps. From this simple example you can clearly see how much more productive compound exercises are for building muscle.

Free Weights VS. Machines

Free weight exercises are more effective for building muscle then machine exercises. Machines make the exercises easier to perform. You do not have to balance the weight with machine exercises because the machine balances the weight for you. You will get less muscle stimulation from machine exercises because they do not require the same concentration or effort as free weight exercises. Free weights have a greater ability to involve stabilizer muscles than machines. Free weights put you in a natural, 3 dimensional environment for exercise.

The majority of your exercises should be compound free weight exercises. This does not mean that you should avoid machine exercises or isolation exercises. They are easy to learn and there is a low risk of injury, which is great for people who are just starting out or for rehabilitation purposes. And there are some good machine exercises that cannot be duplicated with free weights such as various cable pulley exercises. However, the majority of lifters should always base their workouts around compound, free weight exercises and supplement their workouts with machine and isolation exercises.