When I ask the average gym rat whether he squats until his thighs are parallel to the floor, 99.9 percent of the time he says, "Yes." Then I watch him squat. My reaction is almost always the same: Does he understand what "parallel" means? Is he confusing it with "45 degrees"?
I define a proper parallel squat as lowering your body until the tops of your thighs, not the bottoms, are at least parallel to the floor. This small detail typically amounts to at least a 2-inch difference. And when it comes to building muscle, inches matter. That’s because the greater your range of motion, the more muscle fibers you’ll activate, and the bigger you’ll grow. Sure, a shallow squat is less taxing, but shouldn’t that tell you something?
Don’t rely on a mirror to keep you honest; it leaves room for interpretation. Instead, tightly control your depth by squatting with a 12-inch box or a large medicine ball beneath you. (A typical bench doesn’t work, since it stands 18 inches high.) If you’re not touching the box on every repetition, you’re not squatting deep enough.
How to do it: Stand with your heels just in front of a 12-inch box or other object. It can even be a cardboard box, since you won’t be placing your weight on it. Initiate the movement by pushing your hips back. Bend your hips and knees to lower your body until your butt lightly touches the top of the box (don’t sit on it), then press back up to the starting position.