It may have an unglamorous name, but this basic exercise is the favorite of personal trainers everywhere. In fact, squatting is often described as the most effective exercise move of all time. Its appeal lies in the fact that it exercises just about every muscle in the lower half of your body.
If you’ve ever watched championship weight lifting (say, in the Olympics), you’ve seen extreme squatting. Basically, it goes like this—absurdly muscular individuals attempt to stand up with barbells of enormous weight pinned on their backs. While any self-respecting personal trainer can help you do a safe, unintimidating squat, most beginners prefer to start with amodified version of the exercise that doesn’t seem quite so threatening (and doesn’t involve standing under a heavy object).
Here’s how it works:
1. Stand with your feet slightly more than shoulder-width apart. Hold a dumbbell in each hand. (Or, do it without any weights the first time.)
2. Crouch down, while keeping your back straight and breathing in. Stop when your thighs are parallel to the floor (as though you’re sitting in a chair). Don’t let your knees move forward past your toes.
3. Pause, then stand up again, slowly. As you do, look forward and breathe out. This is the step where you really exert yourself.
Source of Information : Oreilly - Your Body Missing Manual