Squats on the Smith Machine

At first doing squats on the Smith felt restrictive - like I was strapped into a carnival ride. Deep into the squat, I felt unusual pressure on my lower back. Then I received some good advice from the trainer at my gym. He pointed out that the feet should not be directly under the shoulders - as it would be during a regular barbell squat. But they should be just in front of the body, so the lifter is slightly leaning back into the rack. During the squat, the knees should never extend out beyond the toes and the thighs never beyond parallel to the floor. Once the thighs pass parallel, pressure is taken off the quads and those muscles are momentarily at rest. It's good advice to do squats on the Smith with just the bar, or very light weights added, until the movement seems more natural.

See a video analysis of the Smith squat at Muscle Ventures.